Make BYPASSRLS behave like superuser RLS bypass.

Make BYPASSRLS behave like superuser RLS bypass.

Specifically, make its effect independent from the row_security GUC, and
make it affect permission checks pertinent to views the BYPASSRLS role
owns.  The row_security GUC thereby ceases to change successful-query
behavior; it can only make a query fail with an error.  Back-patch to
9.5, where BYPASSRLS was introduced.