Additional tests for stored generated columns

Additional tests for stored generated columns

Some additional tests have been created during the development of
virtual generated columns (not included here).  This commit adds
equivalent tests to the existing test set for stored generated
columns.  This includes expanded tests related to MERGE, subqueries,
whole-row references, permissions, domains, partitioning, and
triggers.

Author: Peter Eisentraut <peter@eisentraut.org>
Co-authored-by: jian he <jian.universality@gmail.com>
Co-authored-by: Dean Rasheed <dean.a.rasheed@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/a368248e-69e4-40be-9c07-6c3b5880b0a6@eisentraut.org