Add testing shims to allow switching of app ops/permission backend

Add a shim layer in between the AppOpsService/PermissionManagerService
and their respective implementations. In these shims, include both the
old and new implementations. Select which implementation to use based on
deviceConfig. Also support running both, and comparing the outputs.

Bug: 252886104
Test: manual
Change-Id: Ibe420a1985b041816cb2d6e675761cffa6462f24