R1:f350b9e4646b

Explicitly condition Differential draft promotion on only "impactful" builds

Summary:
Depends on D19281. This increases consistency between build timeline publishing and revision draft promotion.

There's no real behavioral change here (switching how publishing worked already changed the beahvior) but this sends more callsites down the same code paths.

Since the builds we're looking at include completed builds, change the term "active" to "impactful". This describes the same set of builds, but hopefully…