Restore quote and warning behaviors to Differential EditEngine comment area

Summary: Ref T11114. This restores warnings (e.g., failing unit tests) and fixes "Quote" behavior for comments.

Test Plan:

• Quoted a comment.
• Viewed a warning.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11114

Differential Revision: https://secure.phabricator.com/D17117