R1:c4abf160cc51

Fix some file policy issues and add a "Query Workspace"

Summary:
Ref T603. Several issues here:

1. Currently, `FileQuery` does not actually respect object attachment edges when doing policy checks. Everything else works fine, but this was missing an `array_keys()`.
2. Once that's fixed, we hit a bunch of recursion issues. For example, when loading a User we load the profile picture, and then that loads the User, and that loads the profile picture, etc.
3. Introduce a "Query Workspace", which holds…