Method start

packages/plugin-matterjs/lib/PhysicsSystem.ts:103–105

* System 被安装后，所有的 awake 执行完后 * * Called while the System installed, after all of systems' awake been called

()

   * Called while the System installed, after all of systems' awake been called
   */
  start() {
    this.engine.start();
  }
  /**
   * 每一次游戏循环调用，可以做一些游戏操作，控制改变一些组件属性。
   *