R1:70088f7eec8f

Continue reducing callsites to ArcanistDifferentialRevisionStatus

Summary:
Ref T2543. Further consolidates status management into DifferentialRevisionStatus.

One change I'm making here is internally renaming "CLOSED" to "PUBLISHED". The UI will continue to say "Closed", at least for now, but this should make the code more clear because we care about "is closed, exactly" vs "is any closed status (closed, abandoned, sometimes accepted)". This distinction is more obvious as `isClosed()` vs `isPublished()`…