MorphPrimitivesTest.gltf morphs positions but not normals, lighting on morphed mesh looks incorrect

The model [MorphPrimitivesTest.gltf](https://github.com/KhronosGroup/glTF-Sample-Assets/blob/main/Models/MorphPrimitivesTest/glTF/MorphPrimitivesTest.gltf) provides position, normal, and texcoord0 attributes but only morphs positions.
As consequence the morphed mesh uses normals of the flat mesh with all normals pointing to (0,1,0) and the lighting looks incorrect.
This would not happen if the model wouldn't provide normal attributes (resulting in face normals calculated on the morphed positions) or proper morph targets for the normal attribute.

Start by inspecting Models/MorphPrimitivesTest/glTF/MorphPrimitivesTest.gltf and compare its position, normal, texcoord0, and morph-target data. Determine which asset correction is intended; done means the morphed mesh has normals appropriate to its morphed positions and its lighting no longer appears incorrect.

Written by the indexing model from the issue text.