Improve regression test coverage of table lock modes vs permissions.

Improve regression test coverage of table lock modes vs permissions.

Test the interactions with permissions and LOCK TABLE. Specifically
ROW EXCLUSIVE, ACCESS SHARE, and ACCESS EXCLUSIVE modes against
SELECT, INSERT, UPDATE, DELETE, and TRUNCATE permissions. Discussed
by Stephen Frost and Michael Paquier, patch by the latter. Backpatch
to 9.5 where matching behavior was first committed.