Fix pg_dump ACL minimization for PROPERTY GRAPH.

Fix pg_dump ACL minimization for PROPERTY GRAPH.

Adding a GRANT caused pg_dump to emit a useless REVOKE + GRANT of owner
privileges, as seen in a dump of the regression database:

  REVOKE ALL ON PROPERTY GRAPH graph_rls_schema.cabinet FROM nm;
  GRANT ALL ON PROPERTY GRAPH graph_rls_schema.cabinet TO nm;
  GRANT ALL ON PROPERTY GRAPH graph_rls_schema.cabinet TO PUBLIC;

For normal dumps, this has no functional consequences.  For --no-owner
restores, the extra statements may fail or locate unrelated users of the
destination cluster.

The problem was pg_dump assuming NULL relacl implies acldefault('r'),
the default for TABLE.  Fix by teaching acldefault() to retrieve the
PROPERTY GRAPH default ACL.  So pg_dump can still dump from 19beta1, use
acldefault('g') for v20+ only.  For v19, use a hard-coded snapshot of
the v19 default.

information_schema.pg_property_graph_privileges also misused
acldefault('r'), but its "c.prtype IN ('SELECT')" predicate compensated
for it.  Switch to the new acldefault('g') for clarity.  Bump catversion
since a new view won't work with old binaries.  Back-patch to v19, which
introduced PROPERTY GRAPH.

Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/20260630023308.c7.noahmisch@microsoft.com
Backpatch-through: 19