dirstate-map: move most of `dirstate.update_file` logic in the dsmap A new `reset_state` method is introduced to deal with most of that logic. This move things one layer lower, but the ultimate goal is to deal with most of this at the DirstateItem level. This reveal various imperfection with the data passed to update_file by `mergestate.recordupdates`, however this is orthogonal to this patch and should be dealt with at a higher level. Differential Revision: https://phab.mercurial-scm.org/D11134