Ref T12680. See PHI167. See that task for discussion.

Rewrite DiffusionCommitQuery to work more like DifferentialRevisionQuery, and use a UNION to find "all revisions you need to audit OR respond to".

I tried to get this working a little more cleanly than RevisionQuery does, and can probably simplify that now.

Poked at the UI locally without hitting any apparent issues, but my local data is pretty garbage at this point. I'll take a look at how the query plans work on secure.