Mostly provide CSS for "done" states

Summary: Ref T7660. I'm not toggling "inline-state-is-draft" correctly in JS yet since it's a little tricky (you can reload to see it) but the main state should work.

Test Plan:

• Clicked "done", saw comment opacity fade with placeholder style.

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T7660

Differential Revision: https://secure.phabricator.com/D12160