R1:63e6b2553e0e

Simply how Differential drafts ignore Harbormaster autobuilds

Summary:
Ref T2543. When a revision is created, we check if any builds are waiting/failed, and submit it for review immediately if we aren't waiting for anything.

In doing this, we ignore builds with only autotargets, since these are client-side and failures from local `arc lint` / `arc unit` should not count (the user has already chosen to ignore/skip them).

The way we do this has some issues:

- Herald may have started builds, but they…