How to type annotate __main__?

[PeterJCLaw]

At run-time you can import __main__ and it's occasionally useful to do so (for example: jedi does this in utils for setting up REPLs).

While __main__ likely doesn't have a useful members we can put in the typeshed, it could be useful to have it present and importable.

[JelleZijlstra]

What could we put in a stub for __main__ in typeshed? I suppose we could make it an empty file.

[CraftSpider]

Would make sense to have a top-level __getattr__, so it there won't be type complaints. Otherwise yeah, I'd suspect just an empty stub.