Improvements to checkstyle-tester

From discussion at https://github.com/checkstyle/checkstyle/pull/9121#issuecomment-750724281:

> checkstyle/contribution#530 - forgo tests. Looking at https://github.com/checkstyle/checkstyle/blob/master/.ci/no-exception-test.sh#L26-L27, it doesn't look like CI cares if HTML is created or not. It just requires maven to fail the build if it fails. Launch will eventually be removed too.
checkstyle/contribution#524 and checkstyle/contribution#527 - finish PR for new github repos.
checkstyle/contribution#523 - first part of merging launch into diff. lets make this easy and just do copy/paste of what we can. ¿Maybe look into creating groovy tests?
checkstyle/contribution#529 - Complete merging.
checkstyle/contribution#367 - start some removals.
checkstyle/contribution#273 - complete removals.

> I see it as beneficial if we could make it show how the groovy scripts will behave with your new changes... Can you recommend the best way to do this?

> https://groovy-lang.org/testing.html
Testing is going to be new for groovy. This also brings up a thought brought up before. Should we keep this as groovy or is it becoming so complex we should switch it to a Java project.

This issue is simply an umbrella to maintain the order of issues to address, since the original issue where this was discussed (https://github.com/checkstyle/checkstyle/pull/9121#issuecomment-750724281) will be closed.

Start with the ordering and scope listed in this umbrella issue, then review .ci/no-exception-test.sh and the linked discussion in pull request 9121. Check issues 530, 524, 527, 523, 529, 367, and 273 to understand which work remains; done means the planned checkstyle-tester changes and removals are completed in the stated order.

Written by the indexing model from the issue text.