PROPERTY GRAPH pg_dump ACL minimization

pg_dump doesn't do its normal ACL minimization for the new PROPERTY GRAPH
feature. Patch attached. See log message for details.

Most of the patch bulk (modest as it is) exists to keep support for dumping
from beta1. I'm not sure whether it was worth bothering. Breaking dump from
a beta is without precedent known to me, so I just erred on the side of not
breaking it. If we were to decide pg_dump could drop support for betas, I'd
be fine with that.

This entails a catversion bump on the v19 branch. If the master branch
already has a post-branch catversion bump by then, the two catversions should
remain distinct. I'll use yyyymmdd1 for v19 and yyyymmdd2 for master. That
feels cleanest to me, since it uses the *2 value where it will be
shortest-lived. There's precedent in 20b6847 (master) / e256312 (v15).