copies-rust: extract the processing of a ChangedFiles in its own function
This is a reasonably independent piece of code that we can extract in its own
function. This extraction will be very useful for the next changeset, where we
will change the iteration order (but still do the same kind of processing).
Differential Revision: https://phab.mercurial-scm.org/D9421
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}