The `MediaMuxer` (FrameworkMuxer) supports AV1 mime type from API 34.
For this to work track `Format/MediaFormat` must have `CSD`
data.
Change also include providing AV1 option in demo app.
Transmuxing of an AV1 mime type input will not work because
`Extractor` does not extract AV1 CSD data.
Verified changes manually via demo app.
PiperOrigin-RevId: 603002380