Additionally fixes the bugs uncovered in:
  - `MDEV-28332: Alter on temporary table causes ER_TABLE_EXISTS_ERROR note`
    Since there is no `warning` issued by shadowing of base table, this MDEV
    is irrelevant. Keeping for review purposes and for future development
    in case shadowing is going to be implemented
  - `MDEV-28334: SHOW TABLE STATUS shows all temporary tables ignoring database and conditions`
  - `MDEV-28453: SHOW commands are inconsistent for temporary tables`

Reviewed by: <monty@mariadb.org>,
             <vicentiu@mariadb.org>