Adds PolicyRequestProcessor to support new policy checks

This request processor replaces the existing one. The interface
remains the same but adds a new set of dependencies and support
code (see previous commits).

The goal is to provide an easy path for future policy rules
and added capabilities. The first being a new check for special
handling of private profile content.

Bug: 327613051
Test: TODO
Flag: ACONFIG com.android.systemui.screenshot_private_profile DEVELOPMENT
Change-Id: I4f35a4551638f372331922153643e917fa46dee0