Suggestion: split out fidelity tester, maybe move to Khronos Group org, adopt Git LFS

### Description

The fidelity test app is phenomenal. I share it constantly around. I am not sure if it is best in this repository. The repository has a lot of stuff in it. It makes it hard to find the fidelity tester. The fidelity tester also seems to be oriented around model-viewer at first pass, when really it is about the Khronos PBR material model.

Also the fidelity tester makes this repository excessively huge. Even if it doesn't move over to Khronos Group separating it into its own repository would make model viewer more manageable.

We have done similar test suites in the past and we used [Git LFS ](https://docs.github.com/en/repositories/working-with-files/managing-large-files/configuring-git-large-file-storage)for the files. It works quite well. It is a way to keep the repository relatively small and fast while also storing the history. It would be a perfect fit for this use case.