The pg_upgrade check for pg_catalog.unknown type when upgrading from 9.6
had a couple of issues with domains and composite types - it detected
even composite types unused in objects with storage. So for example this
was enough to trigger an unnecessary pg_upgrade failure:

  CREATE TYPE unknown_composite AS (u pg_catalog.unknown)

On the other hand, this only happened with composite types directly on
the pg_catalog.unknown data type, but not with a domain. So this was not
detected

  CREATE DOMAIN unknown_domain AS pg_catalog.unknown;
  CREATE TYPE unknown_composite_2 AS (u unknown_domain);

unlike the first example. These false positives and inconsistencies are
unfortunate, but what's worse we've failed to detected objects using the
pg_catalog.unknown type through a domain. So we missed cases like this

  CREATE TABLE t (u unknown_composite_2);

The consequence is clusters broken after a pg_upgrade.

This fixes these false positives and false negatives by using the same
recursive CTE introduced by eaf900e842 for sql_identifier. Backpatch all
the way to 10, where the of pg_catalog.unknown data type was restricted.

Author: Tomas Vondra
Backpatch-to: 10-
Discussion: https://postgr.es/m/16045-673e8fa6b5ace196%40postgresql.org