pgsql: Fix deparsing of AT TIME ZONE and similar as FROM-clause functio

Fix deparsing of AT TIME ZONE and similar as FROM-clause functions.

ruleutils.c's looks_like_function() assumed that all COERCE_SQL_SYNTAX
cases produce output that looks like a function call (or at least
like one of the syntaxes the func_expr_windowless production accepts).
But AT TIME ZONE, AT LOCAL, OVERLAPS and IS xxx NORMALIZED print as
other sorts of a_expr, so those cases would produce invalid SQL syntax
when used in a FROM clause. Extend the logic to detect which specific
functions are safe or unsafe.

Author: Henson Choi <assam258(at)gmail(dot)com>
Reviewed-by: Prashant Chinnam <crprashant(at)hotmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CAAAe_zC68s-DwVX1o7C1HVcRk+Z+RTS6Vw19auZFfz=KaX8tZA@mail.gmail.com
Backpatch-through: 14

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/17a0604c2d626fa4adb2a98f584fc6b7ee72e663

Modified Files
--------------
src/backend/utils/adt/ruleutils.c | 55 +++++++++++++++++++++++++++++--
src/test/regress/expected/create_view.out | 33 ++++++++++---------
src/test/regress/sql/create_view.sql | 3 +-
3 files changed, 72 insertions(+), 19 deletions(-)