MDEV-14410 - Assertion `table->pos_in_locked_tables == __null ||

             table->pos_in_locked_tables->table == table'
             failed in mark_used_tables_as_free_for_reuse

Assertion failure can be triggered by some DDL executed under LOCK TABLES
that holds lock for DDL target table multiple times (either explicitly or
implcitly).

When closing all table instances for given table (e.g. when preparing for
table removal during CREATE OR REPLACE), only one instance was removed
from m_locked_tables list.

Later we attempt to re-insert one of the instances in mysql_create_table()/
add_back_last_deleted_lock(), which wasn't actually removed. This leads
to m_locks_tables corruption, specifically loss of all following elements.

Then UNLOCK TABLE won't reset some table instances properly (specifically
pos_in_locked_tables), since they're not present in m_locked_tables.

Eventually such table instance gets released to table cache and then
re-used by subsequent statement, which triggers this assertion failure.

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