[Feature Request]: Markdown模式编辑，支持拖拽粘贴等方式添加媒体文件

[Yu-Core]

Is your feature request related to a problem? Please describe. 如题

Describe the solution you'd like 通过js获取file，用互操作传到C#处理

Describe alternatives you've considered Webview拦截处，处理特殊的post请求，貌似比较麻烦