SDK / exoplayer

Allowing duplicate groups caused some other code working with the
array to use reference equality comparison. This is error-prone,
easily forgotten (e.g. when using the TrackGroups in a map) and
causes bugs when TrackGroups are serialized to disk or to another
process.

All TrackGroups created by ExoPlayer are already unique and custom
code creating TrackGroupArrays with identical groups can easily
distringuish them by adding an id to each group.

Issue: google/ExoPlayer#9718
PiperOrigin-RevId: 413617005