Camera2Capturer + onCameraSwitched fix (Android)

[marqroldan]

This should be merged after #452 (I'm assuming this PR gets squashed on merge)

This adds Camera2Capturer based on https://github.com/twilio/video-quickstart-android/blob/master/quickstart/src/main/java/com/twilio/video/quickstart/util/CameraCapturerCompat.java

Tested on the following:

• (Simulator) Android 4.4 (Google APIs)
• (Simulator) Android 10.0 (Google APIs)
• (SM-A715F) Android 11

Changes:

• AndroidX was added

import androidx.annotation.NonNull;
import androidx.annotation.StringDef;
import androidx.annotation.RequiresApi;

• ON_CAMERA_SWITCHED now happens on the camera listener's onCameraSwitched event
• isBackCamera boolean also shows up on onConnected event
• Addition and usage of Camera2Capturer by default based on API level

[slycoder]

@marqroldan Ok I've merged in #452, you should be able to merge master into this branch now.

[marqroldan]

I think I haven't updated the types yet, I shall do that within 24 hours