pgsql: Fix EvalPlanQual rechecking during MERGE.

Fix EvalPlanQual rechecking during MERGE.

Under some circumstances, concurrent MERGE operations could lead to
inconsistent results, that varied according the plan chosen. This was
caused by a lack of rowmarks on the source relation, which meant that
EvalPlanQual rechecking was not guaranteed to return the same source
tuples when re-running the join query.

Fix by ensuring that preprocess_rowmarks() sets up PlanRowMarks for
all non-target relations used in MERGE, in the same way that it does
for UPDATE and DELETE.

Per bug #18103. Back-patch to v15, where MERGE was introduced.

Dean Rasheed, reviewed by Richard Guo.

Discussion: https://postgr.es/m/18103-c4386baab8e355e3%40postgresql.org

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/3c1a1af91d9504e4ce0319f48e83f7c2d5765969

Modified Files
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src/backend/executor/README | 12 +--
src/backend/executor/nodeModifyTable.c | 6 +-
src/backend/optimizer/plan/planner.c | 5 +-
src/include/nodes/execnodes.h | 4 +-
src/include/nodes/plannodes.h | 4 +-
src/test/isolation/expected/merge-join.out | 148 +++++++++++++++++++++++++++++
src/test/isolation/isolation_schedule | 1 +
src/test/isolation/specs/merge-join.spec | 45 +++++++++
src/test/regress/expected/merge.out | 8 +-
src/test/regress/expected/with.out | 42 ++++----
10 files changed, 237 insertions(+), 38 deletions(-)