Add support for danmaku download (Already existing python dependency)

[abcdesteve]

Checklist

• [ ] This feature I'm requesting is already implemented in yt-dlp.
• [ ] This feature is merely a UI/UX update.
• [X] This feature is suitable for primary users with little knowledge about yt-dlp.
• [X] This feature is available for most websites, not only the video platform I use.
• [X] This feature is suitable for a large variety of videos.
• [X] This feature is not going to conflict with many of the existing options.

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

https://github.com/yt-dlp/yt-dlp/issues/8078 This function was not planned in ytdlp repo because it required a 3rd party dependency. But I think it is suitable for seal to add support for it.

Describe the solution you'd like

I would like to have danmaku download together with my video, and I have seen someone successfully converted the xml danmaku file(from bilibili or acfun) into ass subtitle so that it can be displayed properly in any modern video player.

Here's a link for it danmaku2ass It's written in python.

Video link

No response

Additional context

No response

[abcdesteve]

A possible solution was given in yt-dlp#8078.