uncommit: move _movedirstate() to scmutil for reuse The function should be applicable generically when moving from one commit to another. I'll try to add more callers when I find time. I'm not convinced it's handling all the cases correctly, but we should have a generic function for this kind of operation, so I think it belongs somewhere in core (not in the uncommit extension). Differential Revision: https://phab.mercurial-scm.org/D6119