The intent of this patch is to avoid copying arguments from
a pair "Item **args, uint arg_count" to List<Item> in
sp_head::execute_function(). If the number of a stored function parameters
is huge, such copying can affect performance.

Change:
1. Adding a new method Row_definition_list::adjust_formal_params_to_actual_params,
   which accepts a pair of "Item **, uint".
2. Modifying the code to use the new method:
   - the calls for sp_rcontext::retrieve_field_definitions() and
     Row_definition_list::adjust_formal_params_to_actual_params() have
     been moved from sp_rcontext::create() to sp_head::rcontext_create(),
     to handle different argument notations easier (Item** vs List<Item>).
   - sp_rcontext::create() now assumes that the passed Row_definition_list
     is already adjusted to the actual SP parameters, and all "TYPE OF"
     and "ROWTYPE OF" references are resolved.
3. Removing creation of List<Item> in sp_head::execute_procedure(),
   using the code with "Item**, uint" notation instead.
4. Improvement of the code for MDEV-10577:
   As a good side effect, this patch gets rid of double security context
   switch inside sp_head::execute_trigger():
   sp_rcontext is created when the context is already switched,
   so the second context switch inside sp_head::rcontext_create() was
   redundant. This is solved by adding a "bool switch_secutiry_ctx" parameter
   to rcontext_create(), so now execute_function() and execute_procedure()
   pass "true", while execute_trigger() passes "false".

Moving a few methods from sp_rcontext to different classes:

- Table_ident::resolve_table_rowtype_ref
- Qualified_column_ident::resolve_type_ref
- Row_definition_list::resolve_table_rowtype_ref
- Row_definition_list::adjust_formal_params_to_actual_params

It easier to reuse these methods this way in the future.

MDEV-13919 sql_mode=ORACLE: Derive length of VARCHAR SP parameters with no length from actual parameters

Ensure that no adaptive hash index exists for any system tables,
so that the blocked TRUNCATE TABLE t1 will not block the concurrent
TRUNCATE TABLE t2.

Made a few links in README.md secure (https).

This bug is a regression caused by the code refactoring in
commit f5a833c3. It was not present
in any release of the MariaDB server. The bug affects table-rebuilding
ALTER TABLE when the source table is in ROW_FORMAT=REDUNDANT and
contains no virtual columns.

row_log_table_low_redundant(): Log virtual column data only if
virtual columns are present.

The issue was that r_loops, r_rows and r_filtered in ANALYZE FORMAT= JSON were not
calculated for the table on which we were performing the MRR scan in the BKA join
Fixed this by adding respective counter in the JOIN_TAB_SCAN_MRR::open and JOIN_TAB_SCAN_MRR::next

The problem is there is an overflow for the key_file_length.
Added the maximum limit for the key_file_length

The ALTER TABLE…IMPORT TABLESPACE adjustment code that was introduced by
WL#5522 in MySQL 5.6 is incorrectly invoking rec_get_status() on a
ROW_FORMAT=REDUNDANT record to determine if a record is a leaf page record.
The function rec_get_status(rec) is only to be called on
ROW_FORMAT=COMPACT, DYNAMIC or COMPRESSED records.

3-argument form of DATE_FORMAT

Implement Field_timestamp::save_in_field(timestamp_field)
that stores timestamp values without converting them to MYSQL_TIME
and back, because this conversion is lossy around DST change time.
This fixes main.old-mode test.

This is 10.2 version of f8a800be

Implement a special Copy_func function for timestamps, that copies
timestamps without converting them to MYSQL_TIME (the conversion is
lossy around DST change time).

This fixes ALTER TABLE part of main.old-mode test.

This is 10.2 version of f4f48e06

make insert NULL into a timestamp mark the field as having an
explicit value. So that the field won't be assigned the value
again in TABLE::update_default_field()

make Item_func_now_local::save_in_field(timestamp_field) not to go
through MYSQL_TIME - this conversion is lossy around DST change times.
This fixes inserting a default value into a timestamp field.

log_group_read_log_seg(): Only display the message during recovery,
not during normal operation. When the XtraDB configuration parameter
innodb_log_archive is set, this function will be called during
normal operation.

This is a preparatory step for MDEV-13864.
It does not change behavior in any ways. It simply splits methods into smaller peaces.
The intent of this separate patch is to make more readable the main patch for
MDEV-13864 (which will actually move the predicant to args[0]).

1. Splitting fix_length_and_dec() into smaller pieces, adding:
  - bool aggregate_then_and_else_arguments(THD *thd);
  - bool aggregate_switch_and_when_arguments(THD *thd);

2. Splitting find_item() into smaller pieces, adding:
  - Item *find_item_searched();
  - Item *find_item_simple();

3. Splitting print() into smaller pieces, adding:

  - void print_when_then_arguments(String *str, enum_query_type query_type,
                                   Item **items, uint count);
  - void print_else_argument(String *str, enum_query_type query_type, Item *item)

4. Moving the maybe_null handling part related to ELSE from fix_length_and_dec()
   to fix_fields(), as in all other Item_func's.

5. Removing the unused String* argument from find_item().

6. Moving find_item() from public to private, as it's not needed outside.

But without f4f48e06..f8a800be - fixes for MDEV-12672
and related issues. 10.2 specific fix follows...

don't do it via MYSQL_TIME, that conversion is lossy
around DST change dates.

Implement a special Copy_field method for timestamps, that copies
timestamps without converting them to MYSQL_TIME (the conversion
is lossy around DST change dates).

libmariadbclient_18 version nodes, specially for debian builds