Fix pg_upgrade for oid removal.

Fix pg_upgrade for oid removal.

pg_upgrade previously copied pg_largeobject_metadata over from the old
cluster. That doesn't work, because the table has oids before
578b229718. I missed that.

As most pieces of metadata for large objects already were dumped as
DDL (except for comments overwritten by pg_upgrade, due to the copy of
pg_largeobject_metadata) it seems reasonable to just also dump grants
for large objects.  If we ever consider this a relevant performance
problem, we'd need to fix the rest of the already emitted DDL
too.

There's still an open discussion about whether we'll want to force a
specific ordering for the dumped objects, as currently
pg_largeobjects_metadata potentially has a different ordering
before/after pg_upgrade, which can make automated testing a bit
harder.

Reported-By: Andrew Dunstan
Author: Andres Freund
Discussion: https://postgr.es/m/91a8a980-41bc-412b-fba2-2ba71a141c2b@2ndQuadrant.com