Use a policy-aware query in PhabricatorSearchSelectController
Summary: Ref T603. This didn't impact policies anyway, but using PhabricatorObjectQuery is far simpler and more general.
Test Plan: Used "Attach" dialog to find mocks, tasks, and revisions by "Dxx", "Mxx", etc.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T603
Differential Revision: https://secure.phabricator.com/D7195