commitctx: gather more code dealing with copy-in-extra
Now that we have a function that deal with the copy-in-extra special case, we
can gather more code meant to deal with this special case. Making the rest of
the code simpler.
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"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}