changegroup: track changelog to manifest revision map explicitly Previously, self._nextclrevtolocalrev was only populated as part of the changelog lookup callback. But cgpacker._close() was looking at self._nextclrevtolocalrev on every invocation. Since self._nextclrevtolocalrev is for communicating the mapping of changelog revisions to manifest revisions, this commit refactors the code to make that explicit. The changelog state now stores this mapping. And after the changelog group is emitted, we update self._clrevtolocalrev with that dict. self._nextclrevtolocalrev is unused and has been deleted. Differential Revision: https://phab.mercurial-scm.org/D4190