Shader Nodes: Split each node into own file

This improves both code finding,  for example "color ramp" now has its own file.
And now each node has its own namespace so function names can be simplified
similar to rBfab39440e94

This commit also makes all file names use snake case instead of camel case.

Reviewed By: HooglyBoogly

Differential Revision: https://developer.blender.org/D13482

source/blender/blenkernel/intern/node.cc

@@ -5686,7 +5686,7 @@ static void registerShaderNodes()
   register_node_type_sh_wavelength();
   register_node_type_sh_blackbody();
   register_node_type_sh_mix_rgb();
-  register_node_type_sh_valtorgb();
+  register_node_type_sh_color_ramp();
   register_node_type_sh_rgbtobw();
   register_node_type_sh_shadertorgb();
   register_node_type_sh_normal();