refactor(revset): prepare to pass eval hints

`make_pattern_matcher_for_set()` was added in
8ca6b55 to operate on a given set (instead of
all visible commits), so this just adds plumbing so that *all* revset functions
are able to receive an `Option<CommitSet>` which they may use to optimize (or
not) their own evaluation.

Having done that, though, no such hints are actually passed around yet.

Author: claytonrcarter