SDK / exoplayer

Previously only pcm encoding were stored in Format,
this was an issue as for audio passthrough and offload
lots of code needs to pass complex format informations
(encoding, sample rate, channel count, gapless metadata)
but could not use Format and each function was taking
each as different parameter.

By allowing Format to contain any encoding, and not only
pcmEncoding, it allows to pass a Format everywhere in ExoPlayer
code that needs a Format.

This patch does not have any functional change. It is only an internal refactor.

PiperOrigin-RevId: 318789444