Fix mysql_load iterator to skip invisible fields.

MDEV-16100 FOR SYSTEM_TIME erroneously resolves string user variables as transaction IDs

Problem:

Vers_history_point::resolve_unit() tested item->result_type() before
item->fix_fields() was called.

- Item_func_get_user_var::result_type() returned REAL_RESULT by default.
  This caused MDEV-16100.
- Item_func_sp::result_type() crashed on assert.
  This caused MDEV-16094

Changes:
1. Adding item->fix_fields() into Vers_history_point::resolve_unit()
   before using data type specific properties of the history point
   expression.

2. Adding a new virtual method Type_handler::Vers_history_point_resolve_unit()

3. Implementing type-specific
   Type_handler_xxx::Type_handler::Vers_history_point_resolve_unit()
    in the way to:
    a. resolve temporal and general purpose string types to TIMESTAMP
    b. resolve BIT and general purpose INT types to TRANSACTION
    c. disallow use of non-relevant data type expressions in FOR SYSTEM_TIME

    Note, DOUBLE and DECIMAL data types are disallowed intentionally.
    - DOUBLE does not have enough precision to hold huge BIGINT UNSIGNED values
    - DECIMAL rounds on conversion to INT
    Both lack of precision and rounding might potentionally lead to
    very unpredictable results when a wrong transaction ID would be chosen.
    If one really wants dangerous use of DOUBLE and DECIMAL, explicit CAST
    can be used:

      FOR SYSTEM_TIME AS OF CAST(double_or_decimal AS UNSIGNED)

    QQ: perhaps DECIMAL(N,0) could still be allowed.

4. Adding a new virtual method Item::type_handler_for_system_time(),
   to make HEX hybrids and bit literals work as TRANSACTION rather
   than TIMESTAMP.

5. sql_yacc.yy: replacing the rule temporal_literal to "TIMESTAMP TEXT_STRING".
   Other temporal literals now resolve to TIMESTAMP through the new
   Type_handler methods. No special grammar needed. This removed
   a few shift/resolve conflicts.
   (TIMESTAMP related conflicts in "history_point:" will be removed separately)

6. Removing the "timestamp_only" parameter from
   vers_select_conds_t::resolve_units() and Vers_history_point::resolve_unit().
   It was a hint telling that a table did not have any TRANSACTION-aware
   system time columns, so it's OK to resolve to TIMESTAMP in case of uncertainty.
   In the new reduction it works as follows:
   - the decision between TIMESTAMP and TRANSACTION is first made
     based only on the expression data type only
   - then, in case if the expression resolved to TRANSACTION, the table
     is checked if TRANSACTION-aware columns really exist.
   This way is safer against possible ALTER TABLE statements changing
   ROW START and ROW END columns from "BIGINT UNSIGNED" to "TIMESTAMP(x)"
   or the other way around.

This problem occured because the reorganization of the list of values when the
number of elements exceeds 32 was not handled correctly.  I have fixed the
problem by fixing the way that the list values are reorganized when the number
of list values exceeds 32.

Author:
  Jacob Mathew.

Reviewer:
  Alexey Botchkov.

Merged From:
  Branch bb-10.3-MDEV-16101

Forced columns of recursive CTEs to be nullable. SQL standard
requires this only from recursive columns, but in our code
so far we do not differentiate between recursive and non-recursive
columns when aggregating types of the union that specifies a
recursive CTE.

This problem occured because the reorganization of the list of values when the
number of elements exceeds 32 was not handled correctly.  I have fixed the
problem by fixing the way that the list values are reorganized when the number
of list values exceeds 32.

Author:
  Jacob Mathew.

Reviewer:
  Alexey Botchkov.

Problem was that we used table->s->db_type() for accessing
handlerton of opened file instead of table->file->ht

Other bug fixed:
- Ensure that we set error if reopen_tables() fails
  (This was the cause of assert)

The predicate dict_table_is_discarded() checks whether
ALTER TABLE…DISCARD TABLESPACE has been executed.

Replace most occurrences of dict_table_is_discarded() with
checks of dict_table_t::space. A few checks for the flag
DICT_TF2_DISCARDED are necessary; write them inline.

Because !is_readable() implies !space, some checks for
dict_table_is_discarded() were redundant.

Fixed by using exactly the same filtering conditions as specified by standard
in 7.6 <table reference> General Rules

MDEV-14823 Wrong error message upon selecting from a system_time partition
MDEV-15956 Strange ER_UNSUPPORTED_ACTION_ON_GENERATED_COLUMN upon ALTER on versioning column

MDEV-16043 Assertion thd->Item_change_list::is_empty() failed in mysql_parse upon SELECT from a view reading from a versioned table

Lost restore_active_arena().
Using of Query_arena_stmt is suggested instead.

Store transaction start time in thd->transaction.start_time.
THD::transaction_time() wraps over transaction.start_time taking into
account current status of BEGIN.

Don't use hidden system time in versioning,
but keep the system time logic in THD
to workaround low-res system clock and
replication not versioned to versioned.

This reverts MDEV-14788 (System versioning cannot
be based on local timestamps, as it is now).
Versioning is based on local timestamps again,
but timestamps are protected by MDEV-15923
(option to control who can set session @@timestamp).

--secure-timestamp=NO|SUPER|REPLICATION|YES

remove the redundant declaration tail

this is always enabled now,
no need for a conditional

rename LString/XString classes, remove unused ones

Make sure that SELECT_LEX_UNIT::derived, behaves as documented
(points to the "TABLE_LIST representing this union in the
embedding select"). For recursive CTE this was not necessarily
the case, it could've pointed to the TABLE_LIST inside the CTE,
not in the embedding select.

To fix:
* don't update unit->derived in mysql_derived_prepare(), pass derived
  as an argument to st_select_lex_unit::prepare()
* prefer to set unit->derived in TABLE_LIST::init_derived()
  to the TABLE_LIST in the embedding select, not to the recursive
  reference. Fail if there are many TABLE_LISTs in the embedding
  select with conflicting FOR SYSTEM_TIME clauses.

cleanup:
* remove redundant THD* argument from st_select_lex_unit::prepare()

it's internal storage engine error, don't let it leak
into the upper layer.

Make --gdb to take an optional argument *only* if it's
written after '=', not after a space.

followup for 339b9055

In InnoDB, CREATE TEMPORARY TABLE does not allow FULLTEXT INDEX.
Replace a condition with a debug assertion, and add a test.

Problem:

Fix for Bug #21348684 (#Rb9581) introduced a conditional debug execute
'buf_pool_resize_chunk_null', which causes new chunks memory for 2nd
buffer pool instance is freed.

Buffer pool resize function removes all old chunks entry from
'buf_chunk_map_reg' and add new chunks entry into it. But when
'buf_pool_resize_chunk_null' is set true, 2nd buffer pool
instance's chunk entries are not added into 'buf_chunk_map_reg'.
When purge thread tries to access that buffer chunk, it leads to
debug assertion.

Fix:

Added old chunk entries into 'buf_chunk_map_reg' for 2nd buffer pool
instance when 'buf_pool_resize_chunk_null' debug condition is set to true.

Reviewed by: Jimmy <Jimmy.Yang@oracle.com>
RB: 18664

PROBLEM

Issue found during ntest run is a regression of  Bug #27141613. The
issue is basically when index is being freed due to an error during its
creation,when the index isn't added to dictionary cache its field
columns are not set, the derefrencing of null col pointer during the
clean of index from the virtual column's leads to a crash.

NOTE: Also test i_innodb.virtual_debug was failing on 32k page size and
above for the newly added scenario. Fixed that.

FIX

Added a check that if only the index is cached , the virtual index
freeing from the virtual cols index list is performed.

Reviewed by: Satya Bodapati<satya.bodapati@oracle.com>
RB: 18670