SDK / exoplayer

This introduces a new option `setAudioMimeType` in `TranscodingTransformer.Builder` and a corresponding check whether the selected type is supported. This check is done using `supportsSampleMimeType` which is now part of the `Muxer.Factory` and `MuxerWrapper` rather than `Muxer`.
A new field `audioMimeType` is added to `Transformation` and the `TransformerAudioRenderer` uses this instead of the input MIME type if requested.

PiperOrigin-RevId: 405367817