In commit 8ea923f5 (MDEV-24818)
when we optimized multi-statement INSERT into an empty table,
we would sometimes wrongly enable bulk insert into a table that
is actually already using row-level locking and undo logging.

trx_has_lock_x(): New predicate, to check if the transaction of
the current thread is holding an exclusive lock on a table.

trx_undo_report_row_operation(): Only invoke
trx_mod_table_time_t::start_bulk_insert() if
trx_has_lock_x() holds.