Fix #112180: Noise with high detail and lacunarity outputs erratic values

This patch fixes #112180 by aligning the floor fraction function with
the GLSL/SVM ones, through the use of the floor math function.

Pull Request: https://projects.blender.org/blender/blender/pulls/112962

Pull Request: https://projects.blender.org/blender/blender/pulls/131680