Fix docs, PackageInfo_* modules and cabal-version: 3.12

[mpilgrem]

See:

• PackageInfo functionality is not guarded behind cabal-version. #9331

Template B: This PR does not modify behaviour or interface

• Patches conform to the coding conventions. Yes.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions). Not applicable.

[geekosaur]

👍

[geekosaur]

Actually I wonder if it's worth mentioning that putting packages on Hackage that take advantage of 3.10.{1-3} letting you use it could break people with older Cabal versions. That said, I think as part of the above issue's resolution Hackage was upgraded to reject such packages?