This allows changing the display colour of a CollisionShape3D node on a per-shape basis.
It also adds the ability to display a solid coloured preview of a CollisionShape3D.
Closes https://github.com/godotengine/godot-proposals/issues/906
This harmonizes the appearance of collision shapes and paths between
the editor and running project, in both 2D and 3D.
This means that in 3D, paths are now green and shapes are now cyan
instead of light blue.
