Tab completion for \d currently does not complete composite types, even
though \d works for composite types.
That's easy to be fixed, but I have two more general questions:
Since \d is happy to describe any kind of pg_class entry, should we also
remove the relkind restriction in what tab-complete.c currently calls
Query_for_list_of_tisvf? (TOAST tables would also be affected, mainly.)
It looks like this functionality of using \d to show a composite type's
details is not documented at all. Should it be?
describeOneTableDetails() accounts for it, so probably yes.
