Bone.js: Covert to ES6. (#21546)

* Bone: Covert to ES6.

* Add super();

* Clean up.

src/objects/Bone.js

 import { Object3D } from '../core/Object3D.js';
 
-function Bone() {
+class Bone extends Object3D {
 
-	Object3D.call( this );
+	constructor() {
 
-	this.type = 'Bone';
+		super();
 
-}
-
-Bone.prototype = Object.assign( Object.create( Object3D.prototype ), {
+		this.type = 'Bone';
 
-	constructor: Bone,
+	}
 
-	isBone: true
-
-} );
+}
 
+Bone.prototype.isBone = true;
 
 export { Bone };