pg_upgrade: Upgrade sequence data via pg_dump

pg_upgrade: Upgrade sequence data via pg_dump

Previously, pg_upgrade migrated sequence data like tables by copying the
on-disk file.  This does not allow any changes in the on-disk format for
sequences.  It's simpler to just have pg_dump set the new sequence
values as it normally does.  To do that, create a hidden submode in
pg_dump that dumps sequence data even when a schema-only dump is
requested, and trigger that submode in binary upgrade mode.  (This new
submode could easily be exposed as a command-line option, but it has
limited use outside of pg_dump and would probably cause some confusion,
so we don't do that at this time.)

Reviewed-by: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>