added vtkCGALMeshSmoothing filter
as the title says, I added the vtkCGALMeshSmoothing filter
wasn't much work, I simply copied vtkCGALShapeSmoothing and adapted it, using the example from
hope I can contribute more in the future, especially hoping to find some time to look into surface reconstruction from point clouds as described here:
https://doc.cgal.org/latest/Manual/tuto_reconstruction.html#TutorialsReconstruction_algorithms