pgsql: Error out if SKIP LOCKED and WITH TIES are both specified

Error out if SKIP LOCKED and WITH TIES are both specified

Both bugs #16676[1] and #17141[2] illustrate that the combination of
SKIP LOCKED and FETCH FIRST WITH TIES break expectations when it comes
to rows returned to other sessions accessing the same row.  Since this
situation is detectable from the syntax and hard to fix otherwise,
forbid for now, with the potential to fix in the future.

[1] https://postgr.es/m/16676-fd62c3c835880da6@postgresql.org
[2] https://postgr.es/m/17141-913d78b9675aac8e@postgresql.org

Backpatch-through: 13, where WITH TIES was introduced
Author: David Christensen <david.christensen@crunchydata.com>
Discussion: https://postgr.es/m/CAOxo6XLPccCKru3xPMaYDpa+AXyPeWFs+SskrrL+HKwDjJnLhg@mail.gmail.com

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/20047609d39cc4d30d6b266ed3a8b418b3ce5f78

Modified Files
--------------
doc/src/sgml/ref/select.sgml        |  3 ++-
src/backend/commands/matview.c      |  3 ++-
src/backend/parser/gram.y           | 15 +++++++++++++++
src/test/regress/expected/limit.out |  5 +++++
src/test/regress/sql/limit.sql      |  5 +++++
5 files changed, 29 insertions(+), 2 deletions(-)