PrimitiveMesh.flip_faces is compared to wrong cull mode

[thesquaregroot]

Your Godot version:
3.3.2.stable

Issue description:
In PrimitiveMesh, the description of flip_faces seems backwards to me. It mentions that if the flag is set the backside of the mesh is drawn, but then mentions this is the same as using SpatialMaterial.CULL_BACK. I believe this should say SpatialMaterial.CULL_FRONT instead, since the front is culled and the backfaces are drawn. That said, the description of CullMode is also strange, as it mentions backfaces specifically: "Which side of the object is not drawn when backfaces are rendered" -- perhaps that should just say "when faces are rendered"?

URL to the documentation page:
https://docs.godotengine.org/en/stable/classes/class_primitivemesh.html#class-primitivemesh-property-flip-faces
https://docs.godotengine.org/en/stable/classes/class_spatialmaterial.html#class-spatialmaterial-property-params-cull-mode