R1:157f47cd149c

Rewrite CommitQuery to use UNION for performance

Summary:
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.

Test Plan: Poked at the UI locally without hitting any apparent issues, but my local data is pretty garbage at this point. I'll take…