Draft: Generate HasField instances for record selectors with constraints (#22267)

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Please read the checklist below to make sure your contribution fulfills these expectations. Also please answer the following question in your MR description:

Where is the key part of this patch? That is, what should reviewers look at first?

compiler/GHC/Tc/Instance/Class.hs

Please take a few moments to address the following points:

• if your MR touches base (or touches parts of ghc-internal used or re-exported by base) more substantially than just amending comments or documentation, you likely need to raise a CLC proposal before merging it.
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• add a testcase to the testsuite.
• updates the users guide if applicable
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If you have any questions don't hesitate to open your merge request and inquire in a comment. If your patch isn't quite done yet please do add prefix your MR title with WIP:.

Question from the author

• Should I update notes and release note?

Other info

Done during ZuriHac 2025 with the help of @adamgundry thanks so much!

Note: my latop is not powerful enough to compile GHC, I'll try it at home.