pgsql: Expand run-time partition pruning to work with MergeAppend

Expand run-time partition pruning to work with MergeAppend

This expands the support for the run-time partition pruning which was added
for Append in 499be013de to also allow unneeded subnodes of a MergeAppend
to be removed.

Author: David Rowley
Discussion: https://www.postgresql.org/message-id/CAKJS1f_F_V8D7Wu-HVdnH7zCUxhoGK8XhLLtd%3DCu85qDZzXrgg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5220bb7533f9891b1e071da6461d5c387e8f7b09

Modified Files
--------------
doc/src/sgml/perform.sgml | 12 +--
src/backend/executor/nodeAppend.c | 2 +-
src/backend/executor/nodeMergeAppend.c | 137 ++++++++++++++++++++++----
src/backend/nodes/copyfuncs.c | 1 +
src/backend/nodes/outfuncs.c | 2 +
src/backend/nodes/readfuncs.c | 1 +
src/backend/optimizer/plan/createplan.c | 46 +++++++--
src/include/nodes/execnodes.h | 9 ++
src/include/nodes/plannodes.h | 3 +
src/test/regress/expected/partition_prune.out | 137 ++++++++++++++++++++++++++
src/test/regress/sql/partition_prune.sql | 41 ++++++++
11 files changed, 356 insertions(+), 35 deletions(-)