R1:8d8086fccf96

Add Spaces support to Phriction

Summary:
Ref T13164. See PHI774. Fixes T12435.

Since Phriction is hierarchical, there isn't a super strong motivation to support Spaces: you can generally set policies on a small number of documents to get the desired effective policy behavior.

However, it still improves consistency and there's no reason //not// to support Spaces. In the case where you have some moderately weird/complex policy on one or more Spaces, using Spaces to define the policy behavior can make…