pgsql: Avoid failure when altering state of partitioned foreign-key tri

Avoid failure when altering state of partitioned foreign-key triggers.

Beginning in v15, if you apply ALTER TABLE ENABLE/DISABLE TRIGGER to
a partitioned table, it also affects the partitions' cloned versions
of the affected trigger(s).  The initial implementation of this
located the clones by name, but that fails on foreign-key triggers
which have names incorporating their own OIDs.  We can fix that, and
also make the behavior more bulletproof in the face of user-initiated
trigger renames, by identifying the cloned triggers by tgparentid.

Following the lead of earlier commits in this area, I took care not
to break ABI in the v15 branch, even though I rather doubt there
are any external callers of EnableDisableTrigger.

While here, update the documentation, which was not touched when
the semantics were changed.

Per bug #17817 from Alan Hodgson.  Back-patch to v15; older versions
do not have this behavior.

Discussion: https://postgr.es/m/17817-31dfb7c2100d9f3d@postgresql.org

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f61e60102f08305f3cb9e55a7958b8036a02fe39

Modified Files
--------------
doc/src/sgml/ref/alter_table.sgml      | 23 +++++++++++++-------
src/backend/commands/tablecmds.c       |  5 +++--
src/backend/commands/trigger.c         | 38 ++++++++++++++++++++++++----------
src/include/commands/trigger.h         |  3 +++
src/test/regress/expected/triggers.out | 34 ++++++++++++++++++++++++++++++
src/test/regress/sql/triggers.sql      | 15 ++++++++++++++
6 files changed, 98 insertions(+), 20 deletions(-)