These are often the same for image tracks, since we usually drop the
whole image file (both the container and actual encoded image bytes)
into a single sample, but there are cases where we emit a track with
`containerMimeType=image/jpeg` but **no** samples (from
`JpegMotionPhotoExtractor`, to carry some metadata about the image +
video byte offsets).
It's therefore more correct to implement the `supportsFormat` check
based on `sampleMimeType`, so that these 'empty' image tracks are not
considered 'supported' by `ImageRenderer`.
#minor-release
PiperOrigin-RevId: 604672331
eabba49610