Grant "Nearby devices" to Bluetooth MIDI service.

MidiManager.BLUETOOTH_MIDI_SERVICE_PACKAGE is a built-in package
which mediates Bluetooth MIDI connections.  It functions similar to
CompanionDeviceManager and has no UI to request runtime permissions,
since it's proxying operations on behalf of other apps which have
already requested the permission.

Bug: 184920451
Test: manual
Change-Id: Ifd92ba0c701bb3d2aa927cac7c61cb435437444a