PR support KHR_animation_pointer

[DRx3D]

The Sample Models repo had a PR for KHR_animation_pointer. The PR was created by hybridherbst and included a model that tested the extension. This issue is to keep the connection in the new repo. The PR was from https://github.com/prefrontalcortex/glTF-Sample-Models/tree/KHR_animation_pointer

[hybridherbst]

Looks like KHR_animation_pointer has been merged, finally 🎉

• https://github.com/KhronosGroup/glTF/pull/2147

So I'd like to come back to the sample models:

• https://github.com/KhronosGroup/glTF-Sample-Assets/pull/106