urlutil: extract `chain_path` in a function
This will no longer modify `path` inplace so it does not make much sense as a method.
Differential Revision: https://phab.mercurial-scm.org/D10446
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}