postgis_restore.pl autogenerate function signatures for new install

[robe]

As noted in #5348, function signatures are hardcoded

When non-extension dumprestore fails it's probably the postgis_restore.pl script missing knowledge about a signature that should be stripped from the dump. It might be useful to generate part of that list, given our source knows about ANY signature we EVER released in a version we support soft-upgrade from, but those dumps could also come from earlier version, which is why the list we can generate is partial.

This ticket is to support not hard-coding new ones.

[strk]

I think this ticket can be closed, we're generating the restore script skip list now. If any mis-skipped signature is found in the wild it's better to report it as specifically as possible with a new ticket.