iOS13 获取UIWindow

iOS13以后获取UIWindow的方式有调整，需要通过sceneDelegate获取；示例代码如下：

class func currentWindow() -> UIWindow? {
    
    guard #available(iOS 13.0, *) else {
        
        if let appDelegate = UIApplication.shared.delegate,
           let window = appDelegate.window {
            return window
        }
    }
    
    guard let scene = UIApplication.shared.connectedScenes.first,
          let sceneDelegate = scene.delegate as? UIWindowSceneDelegate,
          let window = sceneDelegate.window else {
              return UIApplication.shared.windows.last
          }
    
    return window
}