pg_dump is oblivious to this kind of dependency, so they're lost on
dump/restores (and pg_upgrade).  Have pg_dump emit ALTER lines so that
they're preserved.  Add some pg_dump tests for the whole thing, also.

Reviewed-by: Tom Lane (offlist)
Reviewed-by: Ibrar Ahmed
Reviewed-by: Ahsan Hadi (who also reviewed commit 899a04f5)
Discussion: https://postgr.es/m/20200217225333.GA30974@alvherre.pgsql