Improve Group By SQL Generation by Using Java Formatters

[CanBerker]

Ingo's suggestion:

I don't know whether this is "the Java way", but in other languages I would implement this with a formatter. This way, you only need to test once how to treat each column, set the formatter there, and feed the same formatter in all cases with all possibly needed parameters. Now, you need to do two tests to close the parentheses...

Originally posted by @ingomueller-net in https://github.com/RumbleDB/rumble/pull/655#issuecomment-622940775