Add ability to edit a revision's message

Description of the need

Sometimes when revisions are on by default, no log message is added and you can end up with a lot of revisions with no log message. Then in retrospect, you might find some revisions are referenced more frequently than others, like a page relaunch. It would be nice if an author/editor could update the revision message to make it so they can track that revision more easily.

Proposed solution

Under the node/[nid]/revisions tab, add an operation for "Edit message" or "Edit log" that takes you to node/[nid]/revisions/[vid]/edit-message, that just displays a single textarea for adding/editing a log message.

Alternatives that have been considered

Long-term switching this to a modal would make sense, but we'd need the form and stand-alone page as a non-JS option anyway.

Additional information