zsh_completion: complete files from `hg st -mar` for commit and diff
Useful to have and is consistent with our bash completion file.
This is also an improvement coming from upstream, downstream or sidestream
(depends on how you look at it) hg completion file -- the one that lives in
zsh's own repo.
Differential Revision: https://phab.mercurial-scm.org/D4263
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273ce12ad8f1` will report some style violations on a very old commit).