Expose more Utility Functions from MediaTransformer

MediaTransformer does a really nice job of being very simple to use when you're first getting started.
Once you want advanced functionality however, you are faced with creating your own MediaTarget, MediaFormat, TrackTransforms etc.

There's a lot of nice logic in LiTr that has been written to do exactly that, but a lot of it is private, even if it doesn't have any side effects. When building my own more custom transformer, I found myself copying logic from MediaTransformer (createTargetMediaFormat, isAudioIncompatible, ...) constantly.

I think there is a big opportunity to make LiTr more approachable by exposing more of the Utility that is hidden away inside. Dealing with MediaFormats is both a daunting task for beginners, but also very essential in a lot of cases, so I assume a lot of users would benefit from improving the usability in that regard :)

A first step would be opening up some of the functions that are already there, but on top of that, more utility functions could still be written

Start with MediaTransformer and inspect the existing createTargetMediaFormat and isAudioIncompatible utilities, including their visibility and current callers. Clarify which functions should become public and whether additional utilities are needed; done means the agreed utility API is exposed without requiring users to copy internal logic.