pgsql: Fix some more bugs in foreign keys connecting partitioned tables

Fix some more bugs in foreign keys connecting partitioned tables

* In DetachPartitionFinalize() we were applying a tuple conversion map
to tuples that didn't need one, which can lead to erratic behavior if
a partitioned table has a partition with a different column order, as
reported by Alexander Lakhin. This was introduced by 53af9491a043.
Don't do that. Also, modify a recently added test case to exercise
this.

* The same function as well as CloneFkReferenced() were acquiring
AccessShareLock on a partition, only to have CreateTrigger() later
acquire ShareRowExclusiveLock on it. This can lead to deadlock by
lock escalation, unnecessarily. Avoid that by acquiring the stronger
lock to begin with. This probably dates back to branch 12, but I have
never seen a report of this being a problem in the field.

* Innocuous but wasteful: also introduced by 53af9491a043, we were
reading a pg_constraint tuple from syscache that we don't need, as
reported by Tender Wang. Don't.

Backpatch to 15.

Discussion: https://postgr.es/m/461e9c26-2076-8224-e119-84998b6a784e@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2d5fe514052ad82e46612e4c572f1c999be56a71

Modified Files
--------------
src/backend/commands/tablecmds.c | 38 ++++++++++++-------------------
src/test/regress/expected/foreign_key.out | 9 +++++---
src/test/regress/sql/foreign_key.sql | 10 +++++---
3 files changed, 27 insertions(+), 30 deletions(-)