The command line runner in #2976 finally works, but it is a large change set so
I am planning to split it up. This is the first PR split off from there.
This PR adds a patch to Python to expose pymain_run_python. We cannot use the
public API Py_RunMain for this purpose because it finalizes the Python
interpreter with Py_FinalizeEx when it is done. If we start an async task with
Py_RunMain then it will segfault. pymain_run_python does a large amount of work
and reproducing it is undesirable.
I added an args parameter which accepts command line arguments. The private
entry point pyodide._main._run_main() executes the main Python entrypoint
without shutting down the interpreter and returns the return code.