344108: support replying to review comments

•Add new comment part to editor
•Copy comment part to publish comments dialog
•Clear comment part following successful publish
•Clear outgoing state following successful publish
•Migrate existing reviews to support comments
•Added size hint to publish dialog message editor

Change-Id: Ib07d5c7b190baab34f2eb2ef38141cda25dc41e0
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=344108