python literals via pyodide

[mbostock]

This is roughly the same approach as taken by Grant Nestor, although I made some changes to fix falsey value interpolation and to adopt the recommended/public APIs such as runPythonAsync instead of calling eval_code_async directly.

[mootari]

Should the pyodide instance be exposed so that you can e.g. load micropip?

[mbostock]

Should the pyodide instance be exposed so that you can e.g. load micropip?

I’m not going to do this yet, but we might add this in the future.

[mbostock]

Putting this on hold as, at a minimum, I think we need to update the Observable Inspector to do a better job with PyProxy objects.