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 working.)

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13137

Differential Revision: https://secure.phabricator.com/D19445