ObjectGradient does not work correctly

With colorStyle Theme3D.ColorStyleObjectGradient the gradient is used as a texture in PrincipledMaterial. That approach does not work out-of-the-box, as we need to apply the gradient based on the pixel height in the model.

We have 2 options:

1. Hand-craft (or use blender -magic) the UV coordinates for all our models so that the texture is always applied in the correct way
2. Create a custom material that samples the color from the gradient texture and applies it based on the y position of the fragment in model space

Option #2 would be better, as we should be able to use that directly with all the graph types. Option #1 would work only with bars and scatter, but surface would still need its own shader.