JavaScript (v3): Refactor libs/scenario to use typescript.

[cpyle0819]

The scenario library continue to grow, improve, and shape the way new examples are written. As a side effect of that it's becoming trickier to handle with JS and JSDoc alone. Since all new workflows are going rely on this library, it makes sense to make it as robust and typesafe as possible. Re-writing in TS seems like a good thing to do.