R1:bab35f28e49d

Respect repository identities when selecting author vs auditor actions

Summary:
Depends on D20580. Fixes T13311. When we choose which actions to show a user, we can either show them "auditor" actions (like "raise concern") or "author" actions (like "request verification").

Currently, we don't show "author" actions if you're the author of the commit via an identity mapping, but we should. Use identity mappings where they exist.

(Because I've implemented `getEffectiveAuthorPHID()` in a way that requires…