Apply SDK vars simplification to ExoPlayer

little improvement over too many "def"

Select audio tracks on iOS & ExoPlayer

just added a function which acts like a ternary with fallback option. Hence, less cluttered "def" variables
great to see that lib is supporting already SDK 27

Implement fullscreen for Android MediaPlayer

This only handles the controls portion of fullscreen. It doesn't make the video use the entire screen, that still needs to be done via styles. Will be implemented later

Implements audio track selection on iOS & Android ExoPlayer. The prop mirrors the API for selectedTextTrack.

Document onAudioBecomingNoisy & add iOS support

Document iOS sidecar text tracks

iOS Side loading for captions and offline support

clearSelectionOverride is still required for "default" and "disabled" case as it otherwise continues to show a selected track if it was previously selected

# Conflicts:
#	ios/RCTVideo.m
#	package.json