dirstate: add a `update_file` function This function is the other side of the `set_tracked`/`set_untracked` API revamp. It is to be used when the dirstate is changing its parents during and update or a merge. It states all the information we know about the file so that the dirstate can update its internal data. Unlike the `set_tracked`/`set_untracked` it has not regards for the information previously tracked in the tristate. Differential Revision: https://phab.mercurial-scm.org/D11075