rhg: Add support for `rhg status --copies` Copy sources are collected during `status()` rather than after the fact like in Python, because `status()` takes a `&mut` exclusive reference to the dirstate map (in order to potentially mutate it for directory mtimes) and returns `Cow<'_, HgPath>` that borrow the dirstate map. Even though with `Cow` only some shared borrows remain, the still extend the same lifetime of the initial `&mut` so the dirstate map cannot be borrowed again to access copy sources after the fact: https://doc.rust-lang.org/nomicon/lifetime-mismatch.html#limits-of-lifetimes Additionally, collecting copy sources during the dirstate tree traversal that `status()` already does avoids the cost of another traversal or other lookups (though I haven’t benchmarked that cost). Differential Revision: https://phab.mercurial-scm.org/D11899