R1:8692d673c8ab

Fix minor inline comment header button behaviors

Summary:
Fixes T12806. Ref T12733.

- Don't count synthetic (lint) comments as anything.
- When you begin writing an inline then cancel it, don't count it as anything.
- When we would show "0 / X", just show "X".

Test Plan:
- Viewed a diff with synthetic comments, no button.
- Wrote, then cancelled an inline. No "X comments".
- Clicked / unlicked "Done", saw "X" -> "1 / X".

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12806, T12733…