MDEV-28343: sys.create_synonym_db fails with ER_VIEW_SELECT_TMPTABLE when schema contains temporary tables

- MDEV-28342 raised the error in case temporary table shadows base table
- Now we are allowed to shadow base tables with temporary tables and
`sys.create_synonym_db()` can easily check for existance of temporary table and
ignore view creation, since it is not supported to create view from
temporary table.
Reviewed-by: &lt;monty@mariadb.org&gt;, <vicentiu@mariadb.org>