Fix catalog insertion order for ATTACH PARTITION

Fix catalog insertion order for ATTACH PARTITION

Commit 2fbdf1b38bc changed the order in which we inserted catalog rows
when creating partitions, so that we could remove an unsightly hack
required for untimely relcache invalidations.  However, that commit only
changed the ordering for CREATE TABLE PARTITION OF, and left ALTER TABLE
ATTACH PARTITION unchanged, so the latter can be affected when catalog
invalidations occur, for instance when the partition key involves an SQL
function.

Reported-by: Rajkumar Raghuwanshi
Author: Amit Langote
Reviewed-by: Michaël Paquier
Discussion: https://postgr.es/m/CAKcux6=nTz9KSfTr_6Z2mpzLJ_09JN-rK6=dWic6gGyTSWueyQ@mail.gmail.com