Partially decouple revision broadcasting from revision draft state
Summary:
Depends on D19283. Ref T13110. To enable "Changes Planned + But, Still A Draft" and "Abandoned + But, Never Promoted From Draft" states, decouple the "broadcast" flag from the "draft" state.
Broadcast behavior is now based only on the `shouldBroadcast` flag, and revisions in any state may have this flag.
Revisions gain this flag when created as a non-draft, or when they leave the draft state for the first time.
There are probably still some ways you can get the wrong result here -- maybe abandon + update -- but those can be cleaned up as they arise.
Test Plan: Kinda poked it a bit but I'll vet this more heavily at the end of this sequence.
Maniphest Tasks: T13110
Differential Revision: https://secure.phabricator.com/D19284