Add possibility to get BluetoothDevice from RxBleDevice

[pszklarska]

It'll be helpful to have getter in RxBleDeviceImpl class for bluetoothDevice (e.g. for using combined BLE and classic Bluetooth)

[tatewaki]

This would be nice 👍

my Workaround is reflection:

try {
    Field field = device.getClass().getDeclaredField("bluetoothDevice");
    field.setAccessible(true);
    BluetoothDevice nativeDevice = (BluetoothDevice) field.get(device);
} catch (Exception e) {
     e.printStackTrace();
}

[dariuszseweryn]

Should be possible to use RxBleDevice.getBluetoothDevice() in the next snapshot of the library.