getActiveEditor () {
    let win = this.getActiveWindow()
    if (win && win.type !== WindowType.EDITOR) {
      win = this._windows.get(this._windowActivity.getSecondNewest())
      if (win && win.type === WindowType.EDITOR) {
        return win
      }
      return undefined
    }
    return win
  }
Returns the (last) active editor window or null if no editor is registered.
@returns {EditorWindow|undefined}