R1:a2d3d8edeb93

Move "update related object after commit" to a separate worker in the task queue

Summary:
Depends on D20462. Ref T13276. Currently, the "Message" parser also updates related tasks and revisions when a commit is published.

For PHI1165, which ran into a race with message parsing, I originally believed we needed to separate this logic and lock + yield to avoid the race. D20462 provides what is probably a better approach for avoiding the race.

Still, I think separating these "update related revisions" and…