`TransformerAudioRenderer` reads input and passes `DecoderInputBuffer`s
to the `AudioSamplePipeline`. The `AudioSamplePipeline` handles all
steps from decoding to encoding. `TransformerAudioRenderer` receives
`DecoderInputBuffer`s from the `AudioSamplePipeline` and passes their
data to the muxer.
`AudioSamplePipeline` implements a new interface `SamplePipeline`.
A pass-through pipeline will be added in a future cl.
PiperOrigin-RevId: 407555102
