unstable: use the `_mutablerevs` function when computing content divergent
This is a useful function to get the revision relevant to these computation,
lets make sure all code use it, so that we can improve that `_mutablerevs`
function in a later changeset.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}