Use the curstom _switchCamera API provided by react-native-webrtc to toggle the
camera instead of destroying the current track and creating a new one.
_switchCamera is implemented at a low level, so the track perceives no changes,
thus being a lot faster and less involved since the capturer doesn't need to be
destroyed and re-created.
In addition, don't mirror the video for the back camera.
Ref: https://github.com/oney/react-native-webrtc/pull/235
7c76f124bf