Bind patches, file content and raw diffs bind policies to their originating objects

Summary:
Fixes T4270. When you download raw file content, diffs, and patches we currently give them default (all users) visibility.

Instead, bind them to the repository or revision in question.

(This code could use a bit of cleanup at some point.)

Test Plan: Hit the patch and content download links in Diffusion and the patch download link in Differential, got restricted files with accurate policy bindings.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4270

Differential Revision: https://secure.phabricator.com/D7849