R1:e4e91ebf6f15

In Differential, allow "r" to create comments and "R" to quote

Summary:
Ref T11401. Fixes T5232. Ref T12616.

Partly, this moves more code over to the new stuff.

This also allows "r" to work if you have code selected (not just comments). If you "reply" to code, you start a new comment.

You can "R" a comment to quote it. This just starts a new comment normally if you "R" a block of code. This is sort of a power-user version of "quote" since it seems like it probably doesn't really make sense to put it in…