Finalize release notes for 2.13.0
Finalize release notes for 2.13.0

PiperOrigin-RevId: 355621265

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