WIP: Create a working flake.nix

[srid]

• Bootstrap flake.nix based on haskell-flake, overriding dependencies
• nix build to work
• devShell (nix develop) to work
• HLS to work
• Upstream skylighting Nix
• How should Nix package deal with cabal flags?

[srid]

Got all the dependencies building, as well as the pandoc sources to build, but the installPhase is failing:

$ nix build -L
...
pandoc> Running phase: installPhase
pandoc> Installing internal library xml-light in /nix/store/6hj2lf84wl10hqmymp8xz9m772g6hdw6-pandoc-3.2.1/lib/ghc-9.6.5/lib/aarch64-osx-ghc-9.6.5/pandoc-3.2.1-5gNPAzSbfOpCcG9wr5Jih8-xml-light
pandoc> Installing library in /nix/store/6hj2lf84wl10hqmymp8xz9m772g6hdw6-pandoc-3.2.1/lib/ghc-9.6.5/lib/aarch64-osx-ghc-9.6.5/pandoc-3.2.1-Cyanjkwa9raImcHGQJDkHy
pandoc> mv: missing destination file operand after '/nix/store/6hj2lf84wl10hqmymp8xz9m772g6hdw6-pandoc-3.2.1/share/man/man1/'
pandoc> Try 'mv --help' for more information.
pandoc> /nix/store/ashgigyp2dkvfi1spyl9nsnirvbk67vh-stdenv-darwin/setup: line 140: pop_var_context: head of shell_variables not a function context