R1:615d27c8e97f

Show an additional "Draft" tag on non-broadcasting revisions in a non-draft state

Summary:
Depends on D19284. Ref T13110. It's now possible to get a revision into a "Abandoned + But, Never Promoted From Draft" state. Show this in the header and provide the draft hint above the comment area.

Also, remove `shouldBroadcast()`. The method `getShouldBroadcast()` now has the same meaning.

Finally, migrate existing drafts to `shouldBroadcast = false` and default `shouldBroadcast` to `true`. If we don't do this…