Move metadata from src/setup.cfg to src/pyproject.toml

[tobiasdiez]

Cherry-picked from #38714 for easier review.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit 84de1a5; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[tobiasdiez]

The changes are an unmodified subset of #38714.
-> Author: @mkoeppe

Tests are passing (to the extend that they are normally passing), changes look good to me, thus setting to positive review.
-> Reviewer: @tobiasdiez

[tobiasdiez]

Matthias, this PR was meant to help you get your code in. But sadly you do not seem to be interested in any form of compromise...

Setting this to disputed. Not sure how to count votes since Matthias is both the author as well as the disputer 🤣

[tobiasdiez]

With the meson build now in place, I don't see a point anymore in improving the setup around setuptools. If someone still feels this is worthwhile to do, feel free to reopen.