R1:26d0862f4f6f

Apply the new patch byte size limit to mail patch generation in Differential

Summary: Ref T13137. See PHI592. Depends on D19444. Apply a limit up front to stop patches which are way too big (e.g., 600MB of videos) from generating in the first place.

Test Plan:
- Configured inline patches in git format.
- Created a normal revision, got an inline git patch.
- Created a revision with a 10MB video file, got no inline patch.
- (Added a bunch of debugging stuff to make sure the internal pathway was…