Allow apps with BLUETOOTH permission to control system routing

They can already control system routing via BluetoothManager,
but it allows them to do both Remote and System routing via
MediaRouter2.

Concretely, this change is needed for apps to access the id of
system routes via MediaRouter2 in order to add info to the
output switcher via RouteListingPreference.

Bug: 274894524
Test: atest CtsMediaBetterTogetherTestCases
Test: atest MediaRouter2HostSideTest
Test: atest AudioPoliciesDeviceRouteControllerTest LegacyDeviceRouteControllerTest
Change-Id: If9bbfc7574e637aa4c07701edf1f2b12e27e4f52
Merged-In: If9bbfc7574e637aa4c07701edf1f2b12e27e4f52