Update "AffectedPath" table when a revision's repository changes

Summary:
Ref T13639. There's currently a hard-to-hit bug where editing the "Repository" of a revision doesn't update this index.

Instead: update the index on repository change, not just diff update.

Test Plan:

• Updated a revision, used debug view to see index update.
• Changed repository on a revision, used debug view to see index update.

Maniphest Tasks: T13639

Differential Revision: https://secure.phabricator.com/D21618