xar: add xarMinimal

xarMinimal allows e2fsprogs to build fuse2fs again on Darwin.
See https://github.com/NixOS/nixpkgs/pull/339412.

pkgs/by-name/xa/xar/package.nix

···
   xar,
 }:
 stdenv.mkDerivation (finalAttrs: {
-  pname = "xar";
+  pname = "xar${lib.optionalString (e2fsprogs == null) "-minimal"}";
   version = "498";
 
   src = fetchFromGitHub {

pkgs/top-level/all-packages.nix

···
     zig = buildPackages.zig_0_12;
   };
 
+  # A minimal xar is needed to break an infinite recursion between macfuse-stubs and xar.
+  # It is also needed to reduce the amount of unnecessary stuff in the Darwin bootstrap.
+  xarMinimal = callPackage ../by-name/xa/xar/package.nix { e2fsprogs = null; };
+
   xclip = callPackage ../tools/misc/xclip { };
 
   xcur2png = callPackage ../tools/graphics/xcur2png { };