This commit contains a fix, where the replication write set for a CREATE TABLE
will contain, as certification keys, table names for all FK references.
With this, all DML for the FK parent tables will conflict with the CREATE TABLE
statement.

There is also new test galera.MDEV-27276 to verify the fix.

Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>

- In ha_innobase::prepare_inplace_alter_table(), InnoDB should
check whether the table is empty. If the table is empty then
server should avoid downgrading the MDL after prepare phase.
It is more like instant alter, does change only in dicationary
and metadata.

- Changed few debug test case to make non-empty DDL table