pgsql: Prohibit pushing subqueries containing window function calculati

Prohibit pushing subqueries containing window function calculation to
workers.

Allowing window function calculation in workers leads to inconsistent
results because if the input row ordering is not fully deterministic, the
output of window functions might vary across workers. The fix is to treat
them as parallel-restricted.

In the passing, improve the coding pattern in max_parallel_hazard_walker
so that it has a chain of mutually-exclusive if ... else if ... else if
... else if ... IsA tests.

Reported-by: Marko Tiikkaja
Bug: 15324
Author: Amit Kapila
Reviewed-by: Tom Lane
Backpatch-through: 9.6
Discussion: https://postgr.es/m/CAL9smLAnfPJCDUUG4ckX2iznj53V7VSMsYefzZieN93YxTNOcw@mail.gmail.com

Branch
------
REL_11_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/2ce253cf57b1c3f8100a31f30647449d0b88fe24

Modified Files
--------------
src/backend/optimizer/util/clauses.c | 16 +++++++++++++++-
src/test/regress/expected/select_parallel.out | 26 ++++++++++++++++++++++++++
src/test/regress/sql/select_parallel.sql | 6 ++++++
3 files changed, 47 insertions(+), 1 deletion(-)