GML fractal noise optimization

Had a look at the GML code for generating fractal noise and found a few terms that could be factored out to make the whole thing about 15% faster, at least in my testing. It’s still fairly slow all things considered, and you still probably don’t want to generate large noise textures in GML in real time, but for smaller generations it’s still free performance.

I also added a fallback for platforms that don’t support surface_r32float.