branchcache: rework the `filteredhash` logic to be more generic
We now have a more flexible `key_hashes` tuple. We duplicated various logic in
the V2 and V3 version of the cache as the goal is to start changing the logic
for V3 in the next few changesets.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}