Add json output for CPython tests

[coolreader18]

Related to #1671

[ep12]

See #1838 (example section):
This pr implements the code object co_varnames attribute, but the value differs from the ones cpython and pypy present...

[abitrolly]

Does it produce the result in real-time, or only after the processing is finished?

Is it a custom format, or something like https://chromium.googlesource.com/chromium/src.git/+/master/docs/testing/json_test_results_format.md was used for an inspiration?

[coolreader18]

@abitrolly I'm not sure what you mean by your first question, but as to your second I think it's basically just the data that unittest outputs itself, converted to JSON. I didn't write the runner myself, I modified it from https://github.com/agramian/custom-text-test-runner, so I can't say for certain.

[coolreader18]

@ep12 I'll look into fixing co_varnames separately.