Conduct refactoring in BluetoothRouteProvider.

- BluetoothRouteProvider has been renamed to
  LegacyBluetoothRouteController
- Extracted interface from BluetoothRouteProvider to
make granular changes
- Provide NoOp implementation to reduce null checks

Bug: b/264876378
Test: tested manually
Change-Id: Ibb32ba3a0825fff45ded460f747b3c3b2d14c2dd