Fix policy for platform compat UI

Only show debuggable apps on user builds. Also, only enable changes that
are overrideable.

Bug: 138280620
Bug: 144552011
Test: Settings->Developer Options->App Compatibility Changes on user
	build
Test: atest PlatformCompatDashboardTest
Exempt-From-Owner-Approval: Previously approved
Change-Id: Ibf9611d1809492ebe979fc55f9331daf78ca9b27