Policy - do proper policy queries when updating owners packages in commit workers

Summary: Ref T7094. This makes the underlying class take a $user parameter, and then the worker just hands it an omnipotent user. Said underyling class is the benefactor of a small re-factor, dropping one query per-use, though the single query that now remains is policy-based so maybe its a wash or even worse. Still, gotta love one less query.

Test Plan:
a little tricky to test so some extra thought instead

basic acceptance test with bin/repository reparse --change rValidHashHere -- it worked!

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7094

Differential Revision: https://secure.phabricator.com/D11653