Broken rendering with khronos GLTF PrimitveModeNormalsTest

[MAG-AdrianMeredith]

The official GLTF samples repository has an example https://github.com/KhronosGroup/glTF-Sample-Assets/tree/main/Models/PrimitiveModeNormalsTest which doesn't render correctly on macos m3 max

see attached model

PrimitiveModeNormalsTest.glb.zip

[MAG-AdrianMeredith]

also in playcanvas viewer

[MAG-AdrianMeredith]

Its slightly less broken in webgpu but still incorrect

[mvaligursky]

I improved this in https://github.com/playcanvas/engine/pull/7706 - now it looks the same in both WebGL and WebGPU (in the engine example created for this)

The remaining issue is that those meshes that do not have normals in the glb should render as unlit. In our glb parser we call generateNormals to generate normals for meshes without them. Ideally we would avoid doing this and configure material to not depend on them, but changing this would possibly break many projects, so I'm hesitant to do so.