Refactor the Add menu in the Compositor, with manually created menus,
inspired by Geometry Nodes.
Minor sorting adjustments by splitting categories in groups, with
separators in between groups, and sorted alphabetically. Compositor
node group assets are also populated in the menus.
This is the first part of the re-organization of the Add menu project,
proposal coming in another patch after this.
Pull Request: https://projects.blender.org/blender/blender/pulls/111282
