Add Shader menu rearrange

Currently shader add menu is just alphabetically sorted list.

It bothers me a little that volume and surface shaders and not even shaders (add/mix) are mixed in single list. Well You dont often add shaders but when You do and You are not very familiar (eg. begginer) with those it might be unnecesary time consuming to find the one that You were looking for.

I propose to kinda split them by separators in 4 groups: Combine, surface, volume and other.

Also Principled ones could (but dont have to) could break alphabetical order and be on top or even their own group because they are somewhat special.

With labels?

Edit: Patch with that change: developer.blender.org/D12945