We refactor the descriptor reupload logic to be similar to the v2 logic
where we update a global 'consider_republishing_rend_descriptors' flag
and then we use that to check for hash ring changes during the global
hidden service callbacks.

This fixes bugs where we would inspect the hash ring immediately as we
receive new dirinfo (e.g. consensus) but before running the hidden
service housekeeping events. That was leaving us in an inconsistent
state wrt hsdir indices and causing bugs all around.