Generating PackageInfo_* files for dependencies to retire most usages of CPP.

[Kleidukos]

In order to avoid using CPP and messing with source tooling like formatters and linters, I'd like cabal to provide me with PackageInfo_* modules for my dependencies, so that I may use Template Haskell in order to provide different code snippets based on the version of my dependencies.

Basically, a Haskell rendition of cabal_macros.h, which could perhaps remain useful for use with FFI, but its CPP would not pollute Haskell source code anymore.

[Kleidukos]

Just to mention that this would be in line with what cabal already offers to do implementation-conditional compilation (see https://github.com/Kleidukos/print-api/blob/main/print-api.cabal#L48-L55 and https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13076)