R1:a1ad184ddd8c

Denormalize added and removed line counts for the current diff onto revisions

Summary:
See PHI230. Currently, we denormalize raw line counts onto diffs and revisions, but not added/removed line counts.

I'd like to try a `[---+ ]` sort of size hint element (see D16322 for more) as a general approach to conveying size information at a glance and see how it feels, since I think the raw size number isn't very scannable/useful and it may be a significant improvement to hint about how much of a change is…