Remove hardcoded GHC versions and source them from ghcup yaml file

[tchoutri]

We have to remove the heinous versionList set from the codebase, and get that from a trusted source.

https://github.com/haskell/ghcup-metadata/blob/develop/ghcup-0.0.9.yaml is a good place for this.

Or calling $ ghcup list -t ghc -r and parsing the results might be better.

[linear]

FLORA-265 Remove hardcoded GHC versions and source them from ghcup yaml file

[tchoutri]

@hasufell says:

you have to create an appstate and then run getGHCupInfo:

• https://github.com/haskell/ghcup-metadata/blob/79dd7be5c0c7741aaf57866c69a6b7e61437ddfc/ghcup-gen/Main.hs#L196-L207
• https://github.com/haskell/ghcup-metadata/blob/79dd7be5c0c7741aaf57866c69a6b7e61437ddfc/ghcup-gen/Main.hs#L220
• https://github.com/haskell/ghcup-metadata/blob/79dd7be5c0c7741aaf57866c69a6b7e61437ddfc/ghcup-gen/Validate.hs#L199

So there's some weird scaffolding. But once you have GHCupInfo, you can just use lenses to collect GHC versions:

• https://github.com/haskell/ghcup-hs/blob/36073910cf7e133700f23c5e1d0538f22cbb4989/lib/GHCup/Types.hs#L74-L78
• https://github.com/haskell/ghcup-hs/blob/36073910cf7e133700f23c5e1d0538f22cbb4989/lib/GHCup/Types.hs#L113-L119