Delete the deprecated variable, spider_use_handler and related code.

Spider now does not supports accessing data nodes via handler
statements. Thus, the notion of SQL kinds are no longer useful.
We too discard it.

Reviewed by: Nayuta Yanagisawa

MDEV-27239 Spider: Assertion `thd->transaction->stmt.ha_list == __null || trans == &thd->transaction->stmt' failed in ha_commit_trans on BEGIN WORK after FTWRL

The check on the SQL command type, in ha_spider::external_lock() is deleted
by e954d9de. This resulted in the wrong call of spider_internal_start_trx()
(and thus Ha_trx_info::register_ha()).

I reverted the check and refactored ha_spider::external_lock().

"#ifdef WITH_PARTITION_STORAGE_ENGINE ... #endif" appears frequently
in the Spider code base. However, there is no need to maintain such
ifdefs because Spider is disabled if the partitioning engine is disabled.

Remove unnecessary #ifdefs and dead code in Spider.
ha_spider::start_bulk_insert without uint flags is not used because
handler::ha_start_bulk_insert calls start_bulk_insert for each storage engine
with flags. Therefore, dead code and #ifdef related to
SPIDER_HANDLER_START_BULK_INSERT_HAS_FLAGS have been removed.

use index_first for DESC keys

Remove the dead-code, in Spider, which is related to the Spider's
HandlerSocket support. The code has been disabled for a long time
and it is unlikely that the code will be enabled.

MDEV-26768 Spider table crashes the server after the mysql_list_fields() client's call and produces weird result for SHOW FIELDS.

Suppress errors in ha_spider::info() called from mysqld_show_fields()

Windows builds failed due to the following error:
'#': invalid character: possibly the result of a macro expansion

The commit e954d9de gave different lifetime to wide_share and
partition_handler_share. This introduced the possibility that
partition_handler_share could be accessed even after it was freed.

We stop sharing partitoiin_handler_share and make it belong to
a single wide_handler to fix the problem.

The server crashes due to passing NULL to spider_free().

In some cases, this == pt_handler_share_handlers[0] at the label
error_get_share in ha_spider::open().

In such cases, to nullify pt_handler_share_handlers[0]->wide_handler
is nothing but to nullify this->wide_handler. We should not do this
before freeing this->wide_handler.

Replace
  * select_lex::offset_limit
  * select_lex::select_limit
  * select_lex::explicit_limit
with select_lex::Lex_select_limit

The Lex_select_limit already existed with the same elements and was used in
by the yacc parser.

This commit is in preparation for FETCH FIRST implementation, as it
simplifies a lot of the code.

Additionally, the parser is simplified by making use of the stack to
return Lex_select_limit objects.

Cleanup of init_query() too. Removes explicit_limit= 0 as it's done a bit later
in init_select() with limit_params.empty()

The assertion failed in handler::ha_reset upon SELECT under
READ UNCOMMITTED from table with index on virtual column.

This was the debug-only failure, though the problem is mush wider:
* MY_BITMAP is a structure containing my_bitmap_map, the latter is a raw
 bitmap.
* read_set, write_set and vcol_set of TABLE are the pointers to MY_BITMAP
* The rest of MY_BITMAPs are stored in TABLE and TABLE_SHARE
* The pointers to the stored MY_BITMAPs, like orig_read_set etc, and
 sometimes all_set and tmp_set, are assigned to the pointers.
* Sometimes tmp_use_all_columns is used to substitute the raw bitmap
 directly with all_set.bitmap
* Sometimes even bitmaps are directly modified, like in
TABLE::update_virtual_field(): bitmap_clear_all(&tmp_set) is called.

The last three bullets in the list, when used together (which is mostly
always) make the program flow cumbersome and impossible to follow,
notwithstanding the errors they cause, like this MDEV-17556, where tmp_set
pointer was assigned to read_set, write_set and vcol_set, then its bitmap
was substituted with all_set.bitmap by dbug_tmp_use_all_columns() call,
and then bitmap_clear_all(&tmp_set) was applied to all this.

To untangle this knot, the rule should be applied:
* Never substitute bitmaps! This patch is about this.
 orig_*, all_set bitmaps are never substituted already.

This patch changes the following function prototypes:
* tmp_use_all_columns, dbug_tmp_use_all_columns
 to accept MY_BITMAP** and to return MY_BITMAP * instead of my_bitmap_map*
* tmp_restore_column_map, dbug_tmp_restore_column_maps to accept
 MY_BITMAP* instead of my_bitmap_map*

These functions now will substitute read_set/write_set/vcol_set directly,
and won't touch underlying bitmaps.

The assertion failed in handler::ha_reset upon SELECT under
READ UNCOMMITTED from table with index on virtual column.

This was the debug-only failure, though the problem is mush wider:
* MY_BITMAP is a structure containing my_bitmap_map, the latter is a raw
 bitmap.
* read_set, write_set and vcol_set of TABLE are the pointers to MY_BITMAP
* The rest of MY_BITMAPs are stored in TABLE and TABLE_SHARE
* The pointers to the stored MY_BITMAPs, like orig_read_set etc, and
 sometimes all_set and tmp_set, are assigned to the pointers.
* Sometimes tmp_use_all_columns is used to substitute the raw bitmap
 directly with all_set.bitmap
* Sometimes even bitmaps are directly modified, like in
TABLE::update_virtual_field(): bitmap_clear_all(&tmp_set) is called.

The last three bullets in the list, when used together (which is mostly
always) make the program flow cumbersome and impossible to follow,
notwithstanding the errors they cause, like this MDEV-17556, where tmp_set
pointer was assigned to read_set, write_set and vcol_set, then its bitmap
was substituted with all_set.bitmap by dbug_tmp_use_all_columns() call,
and then bitmap_clear_all(&tmp_set) was applied to all this.

To untangle this knot, the rule should be applied:
* Never substitute bitmaps! This patch is about this.
 orig_*, all_set bitmaps are never substituted already.

This patch changes the following function prototypes:
* tmp_use_all_columns, dbug_tmp_use_all_columns
 to accept MY_BITMAP** and to return MY_BITMAP * instead of my_bitmap_map*
* tmp_restore_column_map, dbug_tmp_restore_column_maps to accept
 MY_BITMAP* instead of my_bitmap_map*

These functions now will substitute read_set/write_set/vcol_set directly,
and won't touch underlying bitmaps.

MDEV-7098 spider/bg.spider_fixes failed in buildbot with safe_mutex: Trying to unlock mutex conn->mta_conn_mutex that wasn't locked at storage/spider/spd_db_conn.cc, line 671

MDEV-7098 spider/bg.spider_fixes failed in buildbot with safe_mutex: Trying to unlock mutex conn->mta_conn_mutex that wasn't locked at storage/spider/spd_db_conn.cc, line 671

MDEV-7098 spider/bg.spider_fixes failed in buildbot with safe_mutex: Trying to unlock mutex conn->mta_conn_mutex that wasn't locked at storage/spider/spd_db_conn.cc, line 671

MDEV-7098 spider/bg.spider_fixes failed in buildbot with safe_mutex: Trying to unlock mutex conn->mta_conn_mutex that wasn't locked at storage/spider/spd_db_conn.cc, line 671

MDEV-7098 spider/bg.spider_fixes failed in buildbot with safe_mutex: Trying to unlock mutex conn->mta_conn_mutex that wasn't locked at storage/spider/spd_db_conn.cc, line 671

MDEV-7098 spider/bg.spider_fixes failed in buildbot with safe_mutex: Trying to unlock mutex conn->mta_conn_mutex that wasn't locked at storage/spider/spd_db_conn.cc, line 671

fix the following type mrr scan
(select 0,`id`,`node` from `auto_test_remote`.`tbl_a` where (`id` <> 0) order by `id`)union all(select 1,`id`,`node` from `auto_test_remote`.`tbl_a` where (`id` <> 0) order by `id`) order by `id`

fix the following type mrr scan
(select 0,`id`,`node` from `auto_test_remote`.`tbl_a` where (`id` <> 0) order by `id`)union all(select 1,`id`,`node` from `auto_test_remote`.`tbl_a` where (`id` <> 0) order by `id`) order by `id`