如何在不覆盖UITabBarItem.appearance()的情况下设置UITabBarAppearance()？

// 创建自定义的UITabBarAppearance对象
let customAppearance = UITabBarAppearance()

// 设置自定义的外观属性
customAppearance.backgroundColor = .white
customAppearance.selectionIndicatorTintColor = .red
customAppearance.stackedLayoutAppearance.normal.titleTextAttributes = [NSAttributedString.Key.foregroundColor: UIColor.black]
customAppearance.stackedLayoutAppearance.selected.titleTextAttributes = [NSAttributedString.Key.foregroundColor: UIColor.red]

// 获取当前的UITabBar实例
if let tabBar = self.tabBar {
    // 获取当前的UITabBarAppearance对象
    if let currentAppearance = tabBar.standardAppearance {
        // 合并自定义的UITabBarAppearance对象与当前的UITabBarAppearance对象
        let mergedAppearance = customAppearance.merge(currentAppearance)
        
        // 将合并后的UITabBarAppearance对象赋值给UITabBar实例的standardAppearance属性
        tabBar.standardAppearance = mergedAppearance
    }
}