Sample skinned assets without inverseBindMatrices

[emackey]

The glTF spec says that inverseBindMatrices are optional.

Does this repo contain any sample assets that use skinning without the IBMs? We should probably have a test asset that checks whether this works in client implementations.

/cc KhronosGroup/glTF#2411

[bghgary]

FWIW, the third model of https://github.com/KhronosGroup/glTF-Asset-Generator/blob/main/Output/Positive/Animation_Skin/README.md is testing this exact thing.

[UltraEngine]

If you have a model you want to try, I can use Unwrap3D to strip out the inverse bind matrices. It works on all models I have tried.