Slices permission model

 - Launcher/assistant get access to all slices
 - Apps with uri access to access a specific slice
 - Apps without access get a permission granting slice
 - If the user authorizes access to the slice for the app
   then the app will be granted access to the app's slices
   (this happens through a temp grant in the service, and a
   full uri grant from the app the next time it binds)
 - Add a hint that apps to add to allow them to return different
   slices depending on the caller, this allows custom permission
   checks.

Test: runtest --path frameworks/base/services/tests/uiservices
Bug: 68751119
Change-Id: I8f8cd0182cfcbfba3f307e2eaba5aae6f6fbe214