R1:463d094f963b

Fix method visibility for `PhabricatorPolicyAwareQuery` subclasses

Summary: Ref T6822.

Test Plan:
`grep` for the following:

- `->willFilterPage(`
- `->loadPage(`
- `->didFilterPage(`
- `->getReversePaging(`
- `->didFilterPage(`
- `->willExecute(`
- `->nextPage(`

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: hach-que, Korvin, epriestley

Maniphest Tasks: T6822

Differential Revision: https://secure.phabricator.com/D11367