Regression test for renamer/typechecker performance (#20261)

This is my first contribution, so please don't hesitate to point out mistakes.

1. Is there a way to test against a previous commit on my end ? As it was not in the code base before, I'm not sure it can be done.
2. I've been unable to run the test case from zachs (https://github.com/zachjs/ghc-issue-20261) because

• building GHC 9.0.1 requires happy 1.19 and I don't know how to "downgrade" mine (happy 1.20)
• usit requires ghcup, which does not seem to be available for FreeBSD

I would be happy to test further, with the proper instructions.

Thanks,