R1:9748520b0e4c

Add "overflow: auto" to all comment boxes

Summary: Set these all to "overflow: auto".

Test Plan:
Made comments like "MMMMMMM..." in:

- Differential comment preview.
- Differential comment (saved).
- Maniphest comment preview.
- Maniphest comment (saved).
- Differential inline comment draft.
- Differential inline comment preview.
- Differential inline comment (saved).

Also tested code blocks.

Reviewers: nh, btrahan, jungejason

Reviewed By: jungejason

CC: aran, epriestley

Maniphest…