Following a similar approach to 703a323.

The CAST(..., BIGINT) for array_agg()'s elements is needed for pg8000.

The previous `if` clause was wrong as it would match the `else` branch
if `default_collation_for_types` was `None` whereas we only want that
branch to match if the type is in `default_collation_for_types` array.

Otherwise, reflection.cache() decorator does not work.

This avoids a join on pg_collation in _domain_query().

We add a `collation_schema` in types supporting `collation`, along with
`postgresql.DOMAIN`, allowing to create respective elements with a
schema-qualified collation name.

Reflection is also handled for both types and domains.

Fix sqlalchemy#9693.