phabricator: teach createdifferentialrevision() to allow a folded commit range
No visible changes here, until an option to enable it is added to `phabsend`.
Differential Revision: https://phab.mercurial-scm.org/D8310
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}