CSG toMesh material required

https://github.com/BabylonJS/Babylon.js/blob/c319ca1cbfa1b249bee93771d4fea1d4279f5e25/src/Mesh/babylon.csg.ts#L590

I think the signature should be:
public toMesh(name: string, material: Nullable<Material>, scene: Scene, keepSubMeshes: boolean): Mesh {

I can PR if you want and that is correct.  thanks.