Make ALTER TRIGGER RENAME consistent for partitioned tables

Make ALTER TRIGGER RENAME consistent for partitioned tables

Renaming triggers on partitioned tables had two problems: first,
it did not recurse to renaming the triggers on the partitions; and
second, it failed to prohibit renaming clone triggers.  Having triggers
with different names in partitions is pointless, and furthermore pg_dump
would not preserve names for partitions anyway.

Not backpatched -- making the ALTER TRIGGER throw an error in stable
versions might cause problems for existing scripts.

Co-authored-by: Arne Roland <A.Roland@index.de>
Co-authored-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Zhihong Yu <zyu@yugabyte.com>
Discussion: https://postgr.es/m/d0fd7040c2fb4de1a111b9d9ccc456b8@index.de