pgsql: Fix filtering of "cloned" outer-join quals some more.

Fix filtering of "cloned" outer-join quals some more.

We've had multiple issues with the clause_is_computable_at logic that
I introduced in 2489d76c4: it's been known to accept more than one
clone of the same qual at the same plan node, and also to accept no
clones at all. It's looking impractical to get it 100% right on the
basis of the currently-stored information, so fix it by introducing a
new RestrictInfo field "incompatible_relids" that explicitly shows
which outer joins a given clone mustn't be pushed above.

In principle we could populate this field in every RestrictInfo, but
that would cost space and there doesn't presently seem to be a need
for it in general. Also, while deconstruct_distribute_oj_quals can
easily fill the field with the remaining members of the commutative
join set that it's considering, computing it in the general case
seems again pretty complicated. So for now, just fill it for
clone quals.

Along the way, fix a bug that may or may not be only latent:
equivclass.c was generating replacement clauses with is_pushed_down
and has_clone/is_clone markings that didn't match their
required_relids. This led me to conclude that leaving the clone flags
out of make_restrictinfo's purview wasn't such a great idea after all,
so add them.

Per report from Richard Guo.

Discussion: https://postgr.es/m/CAMbWs48EYi_9-pSd0ORes1kTmTeAjT4Q3gu49hJtYCbSn2JyeA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/991a3df227e9e8b16d7399df3961dfaae4ae677c

Modified Files
--------------
contrib/postgres_fdw/postgres_fdw.c | 3 +
src/backend/optimizer/README | 15 ++--
src/backend/optimizer/path/equivclass.c | 21 +++++-
src/backend/optimizer/plan/initsplan.c | 55 ++++++++++++--
src/backend/optimizer/util/inherit.c | 10 ++-
src/backend/optimizer/util/orclauses.c | 3 +
src/backend/optimizer/util/relnode.c | 22 ++----
src/backend/optimizer/util/restrictinfo.c | 119 +++++++++++-------------------
src/include/nodes/pathnodes.h | 12 +++
src/include/optimizer/restrictinfo.h | 9 ++-
src/test/regress/expected/join.out | 21 ++++++
src/test/regress/sql/join.sql | 6 ++
12 files changed, 178 insertions(+), 118 deletions(-)