Apply hierarchical policy checks to Phriction

Summary: Ref T4029. When checking the view policy of a document, require the viewer to also be able to see all of the ancestors.

Test Plan:

• Hard-coded /x/y/ to "no one".
  • Checked that /x/y/ is not visible.
  • Checked that /x/y/z/ is not visible.
  • Checked that /x/, /x/q/, etc., are still visible.
• Tested project pages and sub-pages for project visibility.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4029

Differential Revision: https://secure.phabricator.com/D9199