dirstate: move verification code within the dirstate itself This move implementation details further down the stack and make it the verification code easier to discover. Differential Revision: https://phab.mercurial-scm.org/D11526

dirstate-entry: use `?` for the state of entry without any tracking This is what the dirstate use at a higher level. Differential Revision: https://phab.mercurial-scm.org/D11525

dirstate-item: introduce a `any_tracked` property This property is True is the file is tracked anywhere, either the working copy, or any of the parent. Differential Revision: https://phab.mercurial-scm.org/D11524

dirstate-item: introduce a `maybe_clean` property It is useful for some extension that seek to invalidate some state. Differential Revision: https://phab.mercurial-scm.org/D11523

dirstate: add a `get_entry` method to the dirstate This method give access to the underlying `DirstateEntry` object (or an empty one if None was there). It should allow us to use the more semantic property of the entry instead of the state where we needs it. Differential Revision: https://phab.mercurial-scm.org/D11522

dirstate-item: Make constructor parameters optional … in the C implementation of DirstateItem, like they already were in the Python and Rust ones. Differential Revision: https://phab.mercurial-scm.org/D11521

hg-core: silence dead-code warning by adding RevlogEntry::revion() accessor Nightly `rustc` warns about the `RevlogEntry::rev` field not being used. Rather than removing it, I added an accessor since it seems useful to be able to get the entry's revision. Differential Revision: https://phab.mercurial-scm.org/D11548