Uses the same mechanism as when rebuilding changes, except checking
the state of the relevant drafts ref in All-Users.
The one place we couldn't do this easily is in
PatchLineCommentsUtil#draftsByAuthor, since it doesn't have a Change
object available for each change, and we don't want to go overboard in
reading the notes. Just bail and skip rebuilding in that particular
case, marking it as deprecated so it doesn't pick up any new users.
Change-Id: Iaeccc9e665eb6ee2ffa4583f5add8d0ba9968d70
029d256839