This makes it possible to execute `nix-shell` to create the correct environment to build kitty. Use `nix-shell --pure` to eliminate most of the influence of the outside system, e.g. globally installed packages.
This works on NixOS and any Linux or macOS system with the Nix package manager installed.
The build inputs are split into `buildInputs`, `nativeBuildInputs`, `propagatedBuildInputs` and `checkInputs` so it closely resembles 2bb3a9da24/pkgs/applications/terminal-emulators/kitty/default.nix. This makes it easy to port changes between the two files.
