R1:9cb4047134f5

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…