When triggering audits, respect committer identities when importing commits
Summary:
Ref T13311. We currently don't use committer identity mappings when triggering audits, so if a user is only associated with an identity via manual mapping we won't treat them as the author.
Instead, use the identity and manual mapping if they're available.
Test Plan:
- Pushed a commit as `xyz <xyz@example.org>`, an address with no corresponding user.
- In the UI, manually associated that identity with user `@alice`.
- Ran `bin/repository reparse --publish <hash>` to trigger audits and publishing for the commit.
- Before: observed the `$author_phid` was `null`.
- After: observed the `$author_phid` is Alice.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13311
Differential Revision: https://secure.phabricator.com/D20580