localrepo: introduce a `_quick_access_changeid` property
Having faster access to `null` is cuteā¦ but limited. We want to speedup access
to more useful revision, like `.`. We start with turning the fast path for
`null` into something more generic.
Differential Revision: https://phab.mercurial-scm.org/D7488
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}