hg-core: define a `dirstate_status` `Operation` This is 3/3 in a series of patches to improve dirstate status' code. Following in the footsteps of a46e36b82461, we move the main status functionality to an `Operation`. This will most likely be subject to change in the future (what function signature, what parameters, etc., but we will see when `rhg` gets `hg status` support. Differential Revision: https://phab.mercurial-scm.org/D8663