dirstate-item: use `set_possibly_dirty` in `pure.pack_dirstate` Lets make use of the new function. Differential Revision: https://phab.mercurial-scm.org/D11120

dirstate-item: add a `set_possibly_dirty` method See inline documentation for details. The pushes the AMBIGUOUS_TIME implementation further down the line within the DirstateItem only. When this cleanup is done we will be able to stop using this representation internally. Differential Revision: https://phab.mercurial-scm.org/D11119

dirstate-item: add a `from_v1_data` constructor This class method is dedicated to building a DirstateItem from the data available in the "dirstate-v1" format. Since that format is frozen, this constructor will never change (unlike the `__init__` one). Differential Revision: https://phab.mercurial-scm.org/D11118

dirstate-item: use an explicit __init__ function instead of the attrs one For now, this is not doing anything special, however we plan to make it different in the future. So we start simple. Differential Revision: https://phab.mercurial-scm.org/D11117

dirstate: deprecated `drop` outside of `update/merge` All core users have been migrated. Differential Revision: https://phab.mercurial-scm.org/D11116

dirstate: deprecated `remove` outside of `update/merge` All core users have been migrated. Differential Revision: https://phab.mercurial-scm.org/D11115

dirstate: deprecate the `add` method outside of update/merge context All core users have been updated. Differential Revision: https://phab.mercurial-scm.org/D11114

upgrade: avoid a traceback in case of unrecognized revlog Without this, in case of revlog name not matching any know pattern we would get a traceback. Raising a clear error seems simpler. Differential Revision: https://phab.mercurial-scm.org/D11202