Update release notes for 2.16.0
Update release notes for 2.16.0

PiperOrigin-RevId: 407333525

google/ExoPlayer,amzn/exoplayer-amazon-port,amzn/exoplayer-amazon-port,androidx/media,google/ExoPlayer,google/ExoPlayer,androidx/media,androidx/media,amzn/exoplayer-amazon-port