[FR] Deprecate `CSVReporter`

[dmah42]

Is your feature request related to a problem? Please describe. A description of how to deprecate CSVReporter once and for all.

Describe the solution you'd like

• change "output_test_helper.cc" to parse JSON rather than CSV
• add a tool to parse the JSON output into a CSV
• remove CSVReporter and all references to it (just make it build and pass tests)

Describe alternatives you've considered not deprecating it?

Additional context this would cause a major version bump to v2. we have a v2 branch in which some of the above has been attempted but it is very stale.