Add _clone() to Vector2 and to Vector3

src/geometry/vector2.ts

     }
 
     /**
+     * Clone this vector
+     * @returns a clone of this vector
+     * @internal
+     */
+    _clone(): Vector2
+    {
+        return new Vector2(this.x, this.y);
+    }
+
+    /**
      * Normalize this vector
      * @returns this vector, normalized
      * @internal

src/geometry/vector3.ts

     }
 
     /**
+     * Clone this vector
+     * @returns a clone of this vector
+     * @internal
+     */
+    _clone(): Vector3
+    {
+        return new Vector3(this.x, this.y, this.z);
+    }
+
+    /**
      * Normalize this vector
      * @returns this vector, normalized
      * @internal