Fix ordering of GRANT commands in pg_dumpall for tablespaces

This uses a method similar to 68a7c24f and now b8c6014a (applied for
database creation), which guarantees that GRANT commands using the WITH
GRANT OPTION are dumped in a way so as cascading dependencies are
respected.  Note that tablespaces do not have support for initial
privileges via pg_init_privs, so the same method needs to be applied
again.  It would be nice to merge all the logic generating ACL queries
in dumps under the same banner, but this requires extending the support
of pg_init_privs to objects that cannot use it yet, so this is left as
future work.

Discussion: https://postgr.es/m/20190522071555.GB1278@paquier.xyz
Author: Michael Paquier
Reviewed-by: Nathan Bossart
Backpatch-through: 9.6