For the time being we don't support writing a description for those, preferring
having all details in the method's description.
Using self-closing tags saves half the lines, and prevents contributors from
thinking that they should write the argument or return documentation there.
* Removed entirely from RenderingServer.
* Replaced by ImmediateMesh resource.
* ImmediateMesh replaces ImmediateGeometry, but could use more optimization in the future.
* Sprite3D and AnimatedSprite3D work again, ported from Godot 3.x (though a lot of work was needed to adapt them to Godot 4).
* RootMotionView works again.
* Polygon3D editor works again.
