Add sandbox to babel/website plugin docs

[ianjennings]

Every Babel plugin includes an example "in, out, and config" in the docs:

https://babeljs.io/docs/en/babel-plugin-minify-mangle-names

With our sandbox, we'd be able to render these interactively.

• Find out where they are generated from, my guess is babel/website
• Find the plugin string, config, and in properties
• Map these properties into a query string, ex: babelsandbox.com/?plugin=:pluginString&in=:in
• Use the query string to embed an iframe, ex: <iframe src="..."></iframe>
• Hook into the documentation generator to create an iframe within the docs.
• Submit a pull request to babel/web (our site should be live by then)

[garrettluu]

https://github.com/babel/website/tree/master/docs

Parsing the markdown from the website might be more difficult than anticipated due to the inconsistencies between the documentation of different plugins. Most have an example input and output, but some other ones have different formats/explanation like this one

[ianjennings]

Ooooph, ok. Can you:

1. get a count of those we can parse (fit the format)
2. make a list of ones we can do manually

[ianjennings]

We can do this entire ticket manually if need be.

[ianjennings]

I think there are like 130 plugins?