Spherical Harmonics should not be active when mapping scalars

[Meakk]

Describe the bug
When enabling scalar coloring on 3DGS, which can be useful for debugging, spherical harmonics affect the coloring. It shouldn't.

To Reproduce
Steps to reproduce the behavior:

1. Run f3d -osb --coloring-array=scale --point-sprites-type=gaussian --point-sprites-size=1 --no-config hornedlizard_small_d3.spz (file can be found in the testing/data folder)
2. Rotate the camera
3. Observe some gaussians change color

20250707-1951-23.4597438.mp4

Expected behavior
When scalar coloring is enabled, spherical harmonics must be ignored

Additional context
Gaussians rendering is handled in vtkext\private\module\vtkF3DPointSplatMapper.cxx file.
Specifically, spherical harmonics shader is handled in vtkF3DSplatMapperHelper::ReplaceShaderColor.
We need to check if scalar coloring is enabled there to skip the shader modification.

VTK 9.5 is needed for spherical harmonics support.

[Ni-g-3l]

It's strange, I don't have the problem on master

harmonics_gaussian_splat.mp4

[Meakk]

What's your VTK version?

[Ni-g-3l]

What's your VTK version?

9.4.1

[Meakk]

You need VTK 9.5 for spherical harmonics support. I'll add that in the description.