WIP: Better boot lib version scraping

[bergmark]

Ben suggested that we could use https://gitlab.haskell.org/bgamari/ghc-utils/-/raw/master/library-versions/pkg_versions.txt over at https://discourse.haskell.org/t/ghc-9-4-1-rc1-is-now-available/4817/18, rather than scraping the user guide.

Unfortunately the Win32 version is missing there as well!

[snoyberg]

Nice! I'm happy with the overall direction, feel free to merge whenever you're ready.

[mpilgrem]

In respect of this URL, looking at https://gitlab.haskell.org/bgamari/ghc-utils/-/tree/master/library-versions, I think things have moved on. When I put this URL into my browser, I get a 404 error.

[mpilgrem]

I've not been using any script. I manually:

• copy-paste the existing entry for the previous version of GHC;
• look at stack exec -- ghc-pkg list on Windows (for the relevant version of GHC) to see what needs to be changed;
• cross-check the results with the content of the relevant GHC User's Guide, to catch the Linux-specific packages, and to act as a form of quality assurance; and
• try to remember that anything that parses as a YAML number needs to be put in quotes as a YAML string.

As manual tasks go, this is a pretty minor one. It probably takes me less than 10 mins, all told.