pgsql: Fix EPQ run-time pruning using the parent's PARAM_EXEC values

Fix EPQ run-time pruning using the parent's PARAM_EXEC values

8741e48e5 made EvalPlanQualStart() borrow the parent EState's
es_part_prune_states. However, the ExprContext in each
PartitionPruneState belongs to the parent EState, so exec pruning during
an EPQ recheck used the parent's PARAM_EXEC values, i.e. those from the
old row version. This could prune away the partition the recheck
needed, causing the row to be silently skipped, e.g. with a correlated
subquery on a partitioned table in the WHERE clause of an UPDATE.

Here we fix this by giving the EPQ EState its own PartitionPruneStates,
while still borrowing the parent's es_part_prune_results so that the
same subplans are initialized. As the states are no longer shared, the
"initialized" field added by 1b5dd3a24 is no longer needed, so remove
it. This also undoes the ABI break that field caused in 18.

Backpatch to 18, where 8741e48e5 and 1b5dd3a24 were backpatched.

Author: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Reviewed-by: David Rowley <dgrowleyml(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAN4CZFPZ6qKnv6FPmq1RQZ49cHALCwLBu_NJdqUrkZNg0z81JQ%40mail.gmail.com
Backpatch-through: 18

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/57193b3a09ed3555e9c6e3822173427a3249b335

Modified Files
--------------
src/backend/executor/execMain.c | 7 +++-
src/backend/executor/execPartition.c | 42 +++++++++++++++-------
src/include/executor/execPartition.h | 4 +--
.../expected/eval-plan-qual-partition-prune.out | 16 +++++++++
.../specs/eval-plan-qual-partition-prune.spec | 13 ++++++-
5 files changed, 65 insertions(+), 17 deletions(-)