Option to use a more advanced editor for intermediate students

The current state of the editor is very effective in onboarding students into programming.
As students get used to coding and complete the [Intro to JS: Drawing & Animation](https://www.khanacademy.org/computing/computer-programming/programming) course, the more code they are writing as they try to create more complex programs and experiments.

It may be helpful to provide the option to these students to opt into a more featured text editor. Supporting multiple files, smaller text, and intelligence.

An editor like Monaco would suit the purpose: https://microsoft.github.io/monaco-editor/

I'm willing to work on this idea myself if this gets the go signal.

Cheers.

No file, test, or entry point is named. Start by reviewing the existing editor architecture and evaluating Monaco's fit; the issue does not define implementation or acceptance details. Done would require an agreed opt-in advanced editing experience with multiple-file support, smaller text, and intelligence.

Written by the indexing model from the issue text.