Functions 'is_publishable_class' and 'is_publishable_relation' should stay together.

During a recent review, I happened to notice that in the file
src/backend/catalog/pg_publication.c the two functions
'is_publishable_class' and 'is_publishable_relation' used to be [1]
adjacent in the source code. This is also evident in
'is_publishable_relation' because the wording of the function comment
just refers to the prior function (e.g. "Another variant of this,
taking a Relation.") and also this just "wraps" the prior function.

It seems that sometime last year another commit [2] inadvertently
inserted another function ('filter_partitions') between those
aforementioned, and that means the "Another variant of this" comment
doesn't make much sense anymore.

PSA a patch just to put those original 2 functions back together
again. No code is "changed" - only moved.

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[1] https://github.com/postgres/postgres/blame/f0b051e322d530a340e62f2ae16d99acdbcb3d05/src/backend/catalog/pg_publication.c
[2] https://github.com/postgres/postgres/commit/5a2832465fd8984d089e8c44c094e6900d987fcd#diff-1ecc273c7808aba21749ea2718482c153cd6c4dc9d90c69124f3a7c5963b2b4a

Kind Regards,
Peter Smith.
Fujitsu Australia