treewide: Format all Nix files

Format all Nix files using the officially approved formatter,
making the CI check introduced in the previous commit succeed:

  nix-build ci -A fmt.check

This is the next step of the of the [implementation](https://github.com/NixOS/nixfmt/issues/153)
of the accepted [RFC 166](https://github.com/NixOS/rfcs/pull/166).

This commit will lead to merge conflicts for a number of PRs,
up to an estimated ~1100 (~33%) among the PRs with activity in the past 2
months, but that should be lower than what it would be without the previous
[partial treewide format](https://github.com/NixOS/nixpkgs/pull/322537).

Merge conflicts caused by this commit can now automatically be resolved while rebasing using the
[auto-rebase script](8616af08d9/maintainers/scripts/auto-rebase).

If you run into any problems regarding any of this, please reach out to the
[formatting team](https://nixos.org/community/teams/formatting/) by
pinging @NixOS/nix-formatting.

nixos/modules/system/boot/loader/generic-extlinux-compatible/extlinux-conf-builder.nix

@@ -4,7 +4,11 @@ pkgs.replaceVarsWith {
   src = ./extlinux-conf-builder.sh;
   isExecutable = true;
   replacements = {
-    path = lib.makeBinPath [pkgs.coreutils pkgs.gnused pkgs.gnugrep];
+    path = lib.makeBinPath [
+      pkgs.coreutils
+      pkgs.gnused
+      pkgs.gnugrep
+    ];
     inherit (pkgs) bash;
   };
 }