pgsql: Don't create SPLIT/MERGE partitions as internal relations

Don't create SPLIT/MERGE partitions as internal relations

The new partitions built for ALTER TABLE ... SPLIT PARTITION and
ALTER TABLE ... MERGE PARTITIONS are created at the explicit request of
the user, just like a plain CREATE TABLE. createPartitionTable() passes
is_internal=true to heap_create_with_catalog(), while createTableConstraints()
does the same to StoreAttrDefault() and AddRelationNewConstraints().
Pass is_internal=false in all these places instead, so that object-access
hooks treat them as user-requested objects. The is_internal flag is intended
for objects created as internal implementation details, such as a transient
heap built during CLUSTER.

While at it, pass 0 rather than PERFORM_DELETION_INTERNAL to the
performDeletionCheck() calls that pre-check the drop eligibility of the
old partitions, to match the subsequent performDeletion(). The flag has
no functional effect on performDeletionCheck(), but change this for code
consistency.

Reported-by: Noah Misch <noah(at)leadboat(dot)com>
Discussion: https://postgr.es/m/20260707185751.f9.noahmisch@microsoft.com
Backpatch-through: 19

Branch
------
REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6120d01c9f5c985c5154d226181295137e57c552

Modified Files
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src/backend/commands/tablecmds.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)