pgsql: Strip removed-relation references from PlaceHolderVars at join r

Strip removed-relation references from PlaceHolderVars at join removal

When left-join removal deletes a relation, remove_rel_from_query()
updates the relid sets attached to RestrictInfos and
EquivalenceMembers, and the canonical PlaceHolderVar held in each
PlaceHolderInfo, but it does not rewrite the PlaceHolderVars embedded
in clause and EquivalenceClass member expressions. That has been
fine, because later processing consults those relid sets rather than
the embedded PlaceHolderVars.

However, such an expression may afterwards be translated for an
appendrel child and have its relids recomputed from scratch by
pull_varnos(). If the embedded PlaceHolderVar's phrels still mentions
the removed relation, pull_varnos() folds it back in, so the rebuilt
clause's relids reference a no-longer-existent relation. That yields
a parameterized path keyed on the removed relation, tripping the
Assert on root->outer_join_rels in get_eclass_indexes_for_relids().

Fix by stripping the removed relids from the PlaceHolderVars in
surviving rels' baserestrictinfo and in EquivalenceClass member
expressions, keeping them consistent with the canonical
PlaceHolderVars.

This is only reachable on v18 and later, where
match_index_to_operand() began ignoring PlaceHolderVars; before that,
the wrapping PlaceHolderVar prevented the index match that exposes the
stale relids.

Reported-by: Alexander Kuzmenkov <akuzmenkov(at)tigerdata(dot)com>
Author: Richard Guo <guofenglinux(at)gmail(dot)com>
Reviewed-by: Tender Wang <tndrwang(at)gmail(dot)com>
Discussion: https://postgr.es/m/CALzhyqwryL2QywgO03VQr_237Sq3MEVgTTT2_A9G3nGT5-SRZg@mail.gmail.com
Backpatch-through: 18

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/e0252679559adaeee16a7924430f542a1cad3ab7

Modified Files
--------------
src/backend/optimizer/plan/analyzejoins.c | 121 +++++++++++++++++++++++++++---
src/test/regress/expected/join.out | 20 +++++
src/test/regress/sql/join.sql | 12 +++
3 files changed, 143 insertions(+), 10 deletions(-)