Add test cases that reproduce #7241.

Add test cases that reproduce #7241.

- Move project sdist tests to cabal-testsuite
- Add --ignore-project test
- Duplicate tests but without cabal.project
- Add a cabal.project one folder up
- Add a package Z in the root
- Rerun --accept with more immediate parent project
- Add a readme for the tests
- Fix problems with uv package, update expected output
- Add U and V modules
- Explain what is wrong with cabal.dot-uv.test.hs
- Add a note on cabal.no-project.test.hs
- Explain what is wrong with cabal.sub-pq.test.hs
- Explain what is wrong with cabal.sub-rs.test.hs
- Explain what is wrong with cabal.dot-uv.test.hs
- Leave a note explaining cabal.no-project.test.hs
- Leave a note explaining cabal.project.test.hs
- Leave a note explaining cabal.sub-pq.test.hs
- Explain what is wrong with cabal.sub-rs.test.hs
- Patches for project respecting behaviour
- Explain root ignore-project and no-project tests
- Add *.v2.test.hs variants exercising v2-sdist
- Add v2 patches, test out not using <ROOT>