dirstate-item: change the internal storage and constructor value This should be closer to what we do need and what we can actually reliably record. In practice it means that we abandon the prospect of storing much more refined data for now. We don't have the necessary information nor code using it right now. So it seems safer to just use a clearer version of what we had so far. See the documentation changes for details. Differential Revision: https://phab.mercurial-scm.org/D11557