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 "updated related tasks" chunks into separate workers is a net improvement. There may still be some value in doing lock + yield in the future to deal with other issues, and when we occasionally run into problems with pulling a diff out of the repository to update the revision (usually because the diff is too big) this isolates the problem better and allows the commit to import.

I think the only thing to watch out for here is that Herald may now run before the revision and commit are attached to one another. This is fine for all current Herald rules, we just need to be mindful in implementing new rules.

Test Plan: Used bin/repository reparse --message on various commits, including commits that close revisions and close tasks.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13276

Differential Revision: https://secure.phabricator.com/D20463