haskell.packages.ghc942: get inital support up

This change introduces some actual overrides in
configuration-ghc-9.4.x.nix (based on the ones for 9.2) with the aim of
getting a basic 9.4 package set up. In particular the following
“interesting” packages are working:

* hpack
* hoogle
* cabal2nix
* cabal-install

You can get a better overview by looking at the overrides and the
versionedCompilerJobs in release-haskell.nix. Next obvious steps would
be working towards basic HLS support, but it seems that basically none
of the plugins are working so far. Big blockers here:

* alanz/ghc-exactprint#114
* ndmitchell/hlint#1413
* haskell/haskell-language-server#3190

We ourselves have some churn to take care of and should try to release
the changes in NixOS/cabal2nix#571 soon.

Co-authored-by: Rebecca Turner <[email protected]>
Co-authored-by: sternenseemann <[email protected]>

pkgs/top-level/release-haskell.nix

@@ -55,6 +55,7 @@ let
     ghc924
     ghc925
     ghc928
+    ghc942
     ghc945
     ghc946
   ];