Adds a few checks to ensure a debug collision mesh contains mesh data before
attempting to add it to the gizmo draw list. This prevents errors when using
SeparationRayShape3D, which is only intended to draw a single line, and
contains no mesh data.
Closes#100665
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
