[Feature request] Add a way to export a test report json

[tahirmt]

It would be nice to export a json report with screenshots that can provide the test name, file name, file line along with the image names for the reference, failure and difference images.

This information will be handy in creating a report from the xcresult in either html or markdown for use in custom CI.

{
    "file": "/path/to/failed_file.swift",
    "line": 32,
    "message": "failure message reported",
    "attachments": [
        {
            "reference": "file name of image.png",
            "failure": "file name of image.png",
            "difference": "file name of image.png"
        }
    ]
}

[tahirmt]

I see grouping by test is still an option by using --test that gets me a lot of the information I need still