pgsql: Refactor predicate_{implied,refuted}_by_simple_clause.

Refactor predicate_{implied,refuted}_by_simple_clause.

Put the node-type-dependent operations into switches on nodeTag.
This should ease addition of new proof rules for other expression
node types. There is no functional change, although some tests
are made in a different order than before.

Also, add a couple of new cross-checks in test_predtest.c.

James Coleman (part of a larger patch series)

Discussion: https://postgr.es/m/CAAaqYe8Bo4bf_i6qKj8KBsmHMYXhe3Xt6vOe3OBQnOaf3_XBWg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c7076ba6ad1c2dc2ed50496b7ec71daebfe5327c

Modified Files
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src/backend/optimizer/util/predtest.c | 365 ++++++++++++++++---------
src/test/modules/test_predtest/test_predtest.c | 29 ++
2 files changed, 258 insertions(+), 136 deletions(-)