Add run in terminal button to markdown viewer when a code block's language is a shell language

[Tyriar]

[mjbvz]

We need to be very careful that we don't allow markdown previews to run shell scripts without user interaction or allow running script in a potentially confusing way. In untrusted workspaces we should either disable this entirely or at least get user confirmation with a preview of the script to be run

I suggest adding the button using a script that runs after the markdown has been rendered. You can add the script here:

vscode/extensions/markdown-language-features/package.json

Line 743 in 8c363b4

"./media/index.js"

Checkout https://github.com/mjbvz/vscode-markdown-mermaid/blob/master/markdownPreview/index.ts for a more complete example of a script that runs on init and after updates to the md preview

[yelirekim]

I opened a PR for this issue back in December, should I take another go at this? Bother keeping the PR up to date?