The reason for the removal are:
- Generates more code
  - Storing and retreving THD
  - Causes extra code and daata to be generated to handle possible throw
    exceptions (which never happens in MariaDB code)
- Uses more stack space

Other things:
- Changed convert_const_to_int() to use item->save_in_field_no_warnings(),
  which made the code shorter and simpler.
- Removed not needed code in Sp_handler::sp_create_routine()
- Added thd as argument to store_key.copy() to make function simpler
- Added thd as argument to some subselect* constructor that inherites
  from Item_subselect.

- Updated error messages for recovery
- Changed printing of debug sync point information to make it fit 80 char

Other things:
- Updated code comments & fixed indentation
- Removed an old QQ (temporary) comment that does not apply anymore

Author: woqutech

This is needed as we are using uint32 for allocated and current length.

TO_CHAR(expr, fmt)
- expr: required parameter, data/time/timestamp type expression
- fmt: optional parameter, format string, supports
  YYYY/YYY/YY/RRRR/RR/MM/MON/MONTH/MI/DD/DY/HH/HH12/HH24/SS and special
  characters. The default value is "YYYY-MM-DD HH24:MI:SS"

In Oracle, TO_CHAR() can also be used to convert numbers to strings, but
this is not supported. This will gave an error in this patch.

Other things:
- If format strings is a constant, it's evaluated only once and if there
  is any errors in it, they are given at once and the statement will abort.

Original author: woqutech
Lots of optimizations and cleanups done as part of review

MINUS is mapped to EXCEPT
One consequence of the patch is that MINUS becomes a reserved word in
Oracle mode.

Author: woqutech

SYS_GUID() returns same as UUID(), but without any '-'

author: woqutech

The ROWNUM() function is for SELECT mapped to JOIN->accepted_rows, which is
incremented for each accepted rows.
For Filesort, update, insert, delete and load data, we map ROWNUM() to
internal variables incremented when the table is changed.
The connection between the row counter and Item_func_rownum is done
in sql_select.cc::fix_items_after_optimize() and
sql_insert.cc::fix_rownum_pointers()

When ROWNUM() is used anywhere in query, the optimization to ignore ORDER
BY in sub queries are disabled. This was done to get the following common
Oracle query to work:
select * from (select * from t1 order by a desc) as t where rownum() <= 2;
MDEV-3926 "Wrong result with GROUP BY ... WITH ROLLUP" contains a discussion
about this topic.

LIMIT optimization is enabled when in a top level WHERE clause comparing
ROWNUM() with a numerical constant using any of the following expressions:
- ROWNUM() < #
- ROWNUM() <= #
- ROWNUM() = 1
ROWNUM() can be also be the right argument to the comparison function.

LIMIT optimization is done in two cases:
- For the current sub query when the ROWNUM comparison is done on the top
  level:
  SELECT * from t1 WHERE rownum() <= 2 AND t1.a > 0
- For an inner sub query, when the upper level has only a ROWNUM comparison
  in the WHERE clause:
  SELECT * from (select * from t1) as t WHERE rownum() <= 2

In Oracle mode, one can also use ROWNUM without parentheses.

Other things:
- Fixed bug where the optimizer tries to optimize away sub queries
  with RAND_TABLE_BIT set (non-deterministic queries). Now these
  sub queries will not be converted to joins.  This bug fix was also
  needed to get rownum() working inside subqueries.
- In remove_const() remove setting simple_order to FALSE if ROLLUP is
  USED. This code was disable a long time ago because of wrong assignment
  in the following code.  Instead we set simple_order to false if
  RAND_TABLE_BIT was used in the SELECT list.  This ensures that
  we don't delete ORDER BY if the result set is not deterministic, like
  in 'SELECT RAND() AS 'r' FROM t1 ORDER BY r';
- Updated parameters for Sort_param::init_for_filesort() to be able
  to provide filesort with information where the number of accepted
  rows should be stored
- Reordered fields in class Filesort to optimize storage layout
- Added new error messsage to tell that a function can't be used in HAVING
- Added field 'with_rownum' to THD to mark that ROWNUM() is used in the
  query.

Co-author: Oleksandr Byelkin <sanja@mariadb.com>
           LIMIT optimization for sub query

Rename deactivate_ddl_log_entry to ddl_log_increment_phase

Part of prepration for: MDEV-17567 Atomic DDL

No notable code changes except moving code around

DROP TABLE opens all temporary tables at start, but then
uses find_temporary_table() to check if a table is temporary
instead of is_temporary_table() which is much faster.

This patch fixes this issue.

- Moved out creating StringBuffers in loops and instead create them
  outside and just reset the buffer if it was not allocated (to avoid
  a possible malloc/free for every entry)

Other things related to set_buffer_if_not_allocated()
- Changed Valuebuffer to not call set_buffer_if_not_allocated() when
  it is created.
- Fixed geometry functions to reset string length before calling
  String::reserve().  This is because one should not access length()
  of an undefined.
- Added Item_func_conv_charset::save_in_field() as the item is using
  str_value to store cached values, which conflicts with
  Item::save_str_in_field().
- Changed Item_proc_string to not store the string value in sql_string
  as this clashes with Item::save_str_in_field().
- Locally store value of full_name_cstring() in analyse::end_of_records()
  as Item::save_str_in_field() may overwrite it.
- Marked some strings as set_thread_specific()
- Added String::free_buffer() to be used internally in String functions
  to just free the buffer but not reset other String values.
- Fixed uses_buffer_owned_by() to check for allocated length instead of
  strlength, which could be marked MEM_UNDEFINED().

This change removed 68 explict strlen() calls from the code.

The following renames was done to ensure we don't use the old names
when merging code from earlier releases, as using the new variables
for print function could result in crashes:
- charset->csname renamed to charset->cs_name
- charset->name renamed to charset->coll_name

Almost everything where mechanical changes except:
- Changed to use the new Protocol::store(LEX_CSTRING..) when possible
- Changed to use field->store(LEX_CSTRING*, CHARSET_INFO*) when possible
- Changed to use String->append(LEX_CSTRING&) when possible

Other things:
- There where compiler issues with ensuring that all character set names
  points to the same string: gcc doesn't allow one to use integer constants
  when defining global structures (constant char * pointers works fine).
  To get around this, I declared defines for each character set name
  length.

a helper method to check whether an item can be evaluated
in the query optimization phase (in and below JOIN::optimize()).

Other things:
- Remove inline and virtual for methods that are overrides
- Added a 'final' to some Item classes

This returns a LEX_CSTRING and allows one to avoid strlen() calls.

Changes:
- To detect automatic strlen() I removed the methods in String that
  uses 'const char *' without a length:
  - String::append(const char*)
  - Binary_string(const char *str)
  - String(const char *str, CHARSET_INFO *cs)
  - append_for_single_quote(const char *)
  All usage of append(const char*) is changed to either use
  String::append(char), String::append(const char*, size_t length) or
  String::append(LEX_CSTRING)
- Added STRING_WITH_LEN() around constant string arguments to
  String::append()
- Added overflow argument to escape_string_for_mysql() and
  escape_quotes_for_mysql() instead of returning (size_t) -1 on overflow.
  This was needed as most usage of the above functions never tested the
  result for -1 and would have given wrong results or crashes in case
  of overflows.
- Added Item_func_or_sum::func_name_cstring(), which returns LEX_CSTRING.
  Changed all Item_func::func_name()'s to func_name_cstring()'s.
  The old Item_func_or_sum::func_name() is now an inline function that
  returns func_name_cstring().str.
- Changed Item::mode_name() and Item::func_name_ext() to return
  LEX_CSTRING.
- Changed for some functions the name argument from const char * to
  to const LEX_CSTRING &:
  - Item::Item_func_fix_attributes()
  - Item::check_type_...()
  - Type_std_attributes::agg_item_collations()
  - Type_std_attributes::agg_item_set_converter()
  - Type_std_attributes::agg_arg_charsets...()
  - Type_handler_hybrid_field_type::aggregate_for_result()
  - Type_handler_geometry::check_type_geom_or_binary()
  - Type_handler::Item_func_or_sum_illegal_param()
  - Predicant_to_list_comparator::add_value_skip_null()
  - Predicant_to_list_comparator::add_value()
  - cmp_item_row::prepare_comparators()
  - cmp_item_row::aggregate_row_elements_for_comparison()
  - Cursor_ref::print_func()
- Removes String_space() as it was only used in one cases and that
  could be simplified to not use String_space(), thanks to the fixed
  my_vsnprintf().
- Added some const LEX_CSTRING's for common strings:
  - NULL_clex_str, DATA_clex_str, INDEX_clex_str.
- Changed primary_key_name to a LEX_CSTRING
- Renamed String::set_quick() to String::set_buffer_if_not_allocated() to
  clarify what the function really does.
- Rename of protocol function:
  bool store(const char *from, CHARSET_INFO *cs) to
  bool store_string_or_null(const char *from, CHARSET_INFO *cs).
  This was done to both clarify the difference between this 'store' function
  and also to make it easier to find unoptimal usage of store() calls.
- Added Protocol::store(const LEX_CSTRING*, CHARSET_INFO*)
- Changed some 'const char*' arrays to instead be of type LEX_CSTRING.
- class Item_func_units now used LEX_CSTRING for name.

Other things:
- Fixed a bug in mysql.cc:construct_prompt() where a wrong escape character
  in the prompt would cause some part of the prompt to be duplicated.
- Fixed a lot of instances where the length of the argument to
  append is known or easily obtain but was not used.
- Removed some not needed 'virtual' definition for functions that was
  inherited from the parent. I added override to these.
- Fixed Ordered_key::print() to preallocate needed buffer. Old code could
  case memory overruns.
- Simplified some loops when adding char * to a String with delimiters.

This allows us to use String::append() without using strlen().

The changes to the ErrConvString class where done by Alexander Barkov

This patch adds support for right aligned strings and numbers.
Left alignment is left as an exercise for anyone needing it.

MDEV-25612 "Assertion `to <= end' failed in process_args" fixed.
(Was caused by the original version of this patch)

The name change was to make the intention of the flag more clear and
also because most usage of the old flag was to test for
NOT IS_AUTOGENERATED_NAME.

Note that the new flag is the inverse of the old one!

This was done to simplify copying of with_* flags

Other things:
- Changed Flags to C++ enums, which enables gdb to print
  out bit values for the flags. This also enables compiler
  errors if one tries to manipulate a non existing bit in
  a variable.
- Added set_maybe_null() as a shortcut as setting the
  MAYBE_NULL flags was used in a LOT of places.
- Renamed PARAM flag to SP_VAR to ensure it's not confused with persistent
  statement parameters.

One should instead use Item::fixed() and Item::with_subquery()

Removed Item::is_fixed() and has_subquery() and did the following replace:
replace is_fixed() fixed() -- *.*
replace 'has_subquery()' 'with_subquery()' -- *.*

- Added THD argument to functions that calls current_thd() or
  new without a mem_root argument:
  make_same(), set_comparator_func(), set_cmp_func(), set_cmp_func*(),
  set_aggregator() and prepare_sum_aggregators()
- Changed "new Class" to "new (thd->mem_root) Class"

Almost all changes mechanical, no logic changes.

The reason for the change is that neither clang or gcc can do efficient
code when several bit fields are change at the same time or when copying
one or more bits between identical bit fields.
Updated bits explicitely with & and | is MUCH more efficient than what
current compilers can do.

This is a preparation for adding a flags variable to Item class

Added back variable 'with_subquery' to Item class as a bit field.

This made the code shorter, faster (removed some virtual methods,
less code to create an initialized item etc) and made many Item's 7 bytes
smaller.

This is the last set of my patches the decreases the size of Item.

Some examples from gdb:
sizeof(Item):        144 -> 120
sizeof(Item_func)    208 -> 184
sizeof(Item_sum_max) 368 -> 344

Added back variable 'with_sum_func' to Item class as a bit field.

This made the code shorter, faster (removed some virtual methods,
less code to create an initialized item etc) and made many Item's 7 bytes
smaller.

The code is also easier to understand as 'with_sum_func' is threated as any
other Item variable when creating or copying items.

This is to make the Item instances smaller

This was done to have Item::set_maybe_null() as an inline function