GitLab

Optimizations:
* avoid faster ext_table_discovery_simple() *only* when there are
  engines with discover_table_names() method *and* they look at
  file names. P_S implements discover_table_names(), but it's not
  a reason to use slower extension_based_table_discovery().
* don't pre-sort table names if ORDER BY or GROUP BY was specified
* starting from 10.3 only sort table names for SHOW commands