Basic support for subtitles and audio tracks

[StaehliJ]

As a user I want to be able to see subtitles and audio tracks available for some content, as well as to select / deselect a track.

Acceptance criteria

• An API is provided to list available subtitles and audio tracks.
• An API is provided to list the current subtitle and audio track selection.
• An API is provided to select a track (or remove selection if this makes sense).
• Forced subtitles must not treated in a special way.
• The behavior is correct when no subtitles or audio tracks are available.

Documentation

See official documentation.

Hints

There is multiple way to select text and audio tracks. One is to override the selection for a given track, the other is to set preferred language or role to the TrackSelector.

Tasks

• Add API to list available subtitles and audio tracks (forced subtitles not filtered).
• Add API to change the current track selection (basic, no automatic mode).
• Display menu in the demo.