Resolve "Split RayTracedVolume_FP.glsl into VR and IDVR"

What does this MR do?

This MR factorizes some function in RayTracedVolume_FP.glsl, it also refactors glsl files to use our coding style in related files.

How to test it?

Launch OgreViewer and check that nothing has changed when you open and change an image's parameters.

Data

Use any vtk images.

Additional tests to run

• Build on MacOS (Since glsl files has changed)

Associated Issues/Merge Requests

• Issues
  • Closes #250 (closed)