Slightly different, but there is now an VSCode extension to use draw.io directly in the editor.

https://marketplace.visualstudio.com/items?itemName=hediet.v...

If you don't know draw.io, it's an free diagram software that not only has an XML format to save them, but can also be used to save it as a PNG that EMBEDS said XML, so you can edit it again, but display it like a regular image.