Allow Android users to use Seek with front-facing cameras

[albullington]

Teachers sometimes ask us for front-facing camera functionality. Certain Chromebooks, which are popular in the classroom, only have front-facing cameras and therefore can’t access the AR camera.

If there's a reliable way to detect a device which only has a front-facing camera and automatically select that in native code, that would keep things simple for our users.

If that's not an option, we can implement the front-facing camera based on the example from react-native-camera. In this example, a user can toggle between the front and back camera in the camera UI. Their preferred camera type is then passed to the native camera via props.