dirstate-entry: add a `from_p2` property Lets start to define and use more semantic property. Differential Revision: https://phab.mercurial-scm.org/D10956

dirstate-entry: add a `merged` property Lets start to define and use more semantic property. Differential Revision: https://phab.mercurial-scm.org/D10955

dirstate-entry: add a `state` property (and use it) This replace the [0] access. Ultimately is we should probably get ride of this in its current form. However this is a good transitional solution to move away for tuple indexing for now. Differential Revision: https://phab.mercurial-scm.org/D10954

dirstate: move most of the `remove` logic with dirstatemap `removefile` This code deal with special logic to preserving "merged" and "from_p2" information when removing a file. These are implementation details that are more suitable for the dirstatemap layer. Since the dirstatemap layer alreaday have most of the information necessary to do so, the move is easy. This move helps us to encapsulate more implementation details within the dirstatemap and its entry. Easing the use of a different storage for dirstate v2. Differential Revision: https://phab.mercurial-scm.org/D10953

dirstate: add a `in_merge` property This factor the "p2 is not null" check and is fairly simpler to read. Differential Revision: https://phab.mercurial-scm.org/D10952

dirstate-entry: introduce dedicated accessors for v1 serialization In the spirit of changing the content and storage of the dirstate entry, we add new method that the code doing v1 serialisation can use. Adding such method to the C object is quite trivial. Differential Revision: https://phab.mercurial-scm.org/D10951