Sideloaded text tracks & include text track info in onLoad

[cobarx]

This adds the ability to sideload text tracks in Android ExoPlayer. Text tracks must be loaded at the same time the source is set, adding text tracks later will cause the video to reload.

Unfortunately, iOS doesn't support sideloading text tracks without using additional dependencies.

The format for specifying text tracks is:

textTracks={[
  {
    index: 0
    title: "English CC",
    language: "en",
    type: "text/vtt",
    uri: "..."
  },
  {
    index: 1
    title: "Spanish Subtitles",
    language: "es",
    type: "application/x-subrip",
    uri: "..."
  }
]}

Sideloaded text tracks can co-exist side-by-side with embedded captions or captions loaded in an HLS playlist.

Text tracks are also reported as part of the onLoad payload in the textTracks payload. This is support on iOS & Android ExoPlayer.

I will add documentation for this shortly.