Separate remaining cabal tests into their own packages

The problem (https://github.com/haskell/cabal/pull/8398#issuecomment-1231819585) is that cabal package(s) on Hackage mention tests in the .cabal file(s), but they fail building. I think it's easier (also in terms of maintenance) and good enough to just separate them out instead of making sure they remain buildable in each release. The main test suite is separate anyway. We could leave in a single smoke test that distros can use to test their packages.