MDEV-31792 Assertion fails in MDL_context::acquire_lock upon parallel replication of CREATE SEQUENCE

The assert's reason was in missed FL_DDL flagging of CREATE-or-REPLACE
Query event.
MDEV-27365 fixes covered only the non-pre-existing table execution branch so
did not see a possibility of implicit commit in
the middle of execution in a rollback branch when the being CREATEd
sequence table is actually replaced.
The pre-existing table branch cleared the DDL modification
flag so the query lost FL_DDL in binlog and its parallel execution
on slave may have ended up with the assert to indicate the query
is raced by a following in binlog order event.

Fixed with applying the MDEV-27365 pattern.
An mtr test is added to cover the rollback situation.
The description test [ pass ] with a generous number of mtr parallel
reties.