`BKE_pose_rebuild()` should (ideally) always trigger a rebuild of the
depsgraph, since it can add or remove posechannels.
This function now takes a Main parameter to ensure that related
depsgraphes are tagged as dirty (kept it optional, for some corner cases).
We should also probably double-check calls to that function, think in
theory it should only be called from depsgraph itself? But for now...
c205de0203