Allow cancelled inlines, edits, and replies to be undone to get the text back again

Summary: Ref T12616. The ability to do Edit → Cancel → Undo to get your text back on inlines got dropped during the conversion. Restore it.

Test Plan:
Created, replied, and edited inlines, typed text, then cancelled. Was able to undo.

Also undid normal deletion.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12616

Differential Revision: https://secure.phabricator.com/D17916