Use flat normals if normal attribute is not found

[PravinKumar95]

What problem does this solve or what need does it fill?

Most cad/cae files does not contain normals to reduce data. Bevy panics if normals aren't found

What solution would you like?

Use flat normals if normal attribute is not found

What alternative(s) have you considered?

Using a custom shader would solve the issue

Additional context

[jakobhellermann]

This is already done in the main branch: #1808

[mockersf]

As mentioned above, this is done in the GLTF loader, but it still fails for a mesh from another source

[PravinKumar95]

Why not calculate flat normals in the shader if normal attribute is not found. Why do we need to create extra vertex data?

[PravinKumar95]

I think this addressed in 0.6 release. Closing for now