Provide an alternative to --result-log #4488

After discussion in #4447 (comment), @RonnyPfannschmidt mentions he would like to provide a replacement to --result-log in the core before removing it (#3081).

This potentially is an easy contribution given that we have the resultlog.py plugin already which can be used as a starting point.

I would like for us to discuss how that "log file" will look like in this issue.

I understand the rationale is to provide a line-based log file, which can be parsed using standard tools.

I have used a log file in the past where each line was a JSON object, something like:

{"progress": 0.25, "status": "Running simulation"}
{"progress": 0.30, "status": "Running simulation"}
...

pytest would then write each line to the file during pytest_runtest_logreport, like resultlog.py does now.

I suppose we also want to add an option to replay the tests in a log file, so users can reproduce a previous run that was saved to a log?

@RonnyPfannschmidt you also mentioned that pytest-tap would not be an appropriate replacement, can you elaborate on why?