Embed-widget code previews for use in docs

[mofojed]

We should be able to link to an embed widget URL that runs a snippet of code and displays the result. Some suggestions to investigate:

• Query parameter code that takes a base64 encoded string and runs it, then displays the result (similar to something like Monaco playground with their code links)
• POST message with the code
  • May need a separate endpoint
• IFrame postMessage to the embed widget
• Something else?

[vbabich]

There should be a param to select which objects to show and in what order.