Notification 构造函数
实现
factory Notification(String title,
{String? dir, String? body, String? lang, String? tag, String? icon}) {
var parsedOptions = {};
if (dir != null) parsedOptions['dir'] = dir;
if (body != null) parsedOptions['body'] = body;
if (lang != null) parsedOptions['lang'] = lang;
if (tag != null) parsedOptions['tag'] = tag;
if (icon != null) parsedOptions['icon'] = icon;
return Notification._factoryNotification(title, parsedOptions);
}