R1:b6ba75d991df

Add a Phriction hint when a draft exists, and fix some draft editing bugs

Summary:
Depends on D19662. Ref T13077. See PHI840.

- If you're looking at the published version of a document, but a draft version exists and you can edit it, add a hint/link.
- Fix an issue where the "draft" transaction would complain when you created a document since the initial content is empty and no "draft" transaction is adding any content.

Test Plan: Created new documents, viewed documents with current published…