agda.withPackages: add libraryFile to passthru

pkgs/build-support/agda/default.nix

···
       ghc ? ghcWithPackages (p: with p; [ ieee754 ]),
     }:
     let
-      library-file = mkLibraryFile pkgs;
+      libraryFile = mkLibraryFile pkgs;
       pname = "agdaWithPackages";
       version = Agda.version;
     in
···
         nativeBuildInputs = [ makeWrapper ];
         passthru = {
           unwrapped = Agda;
-          inherit withPackages;
+          inherit
+            withPackages
+            libraryFile
+            ;
           tests = {
             inherit (nixosTests) agda;
             allPackages = withPackages (filter self.lib.isUnbrokenAgdaPackage (attrValues self));
···
         mkdir -p $out/bin
         makeWrapper ${lib.getExe Agda} $out/bin/agda \
           ${lib.optionalString (ghc != null) ''--add-flags "--with-compiler=${ghc}/bin/ghc"''} \
-          --add-flags "--library-file=${library-file}"
+          --add-flags "--library-file=${libraryFile}"
         ln -s ${lib.getExe' Agda "agda-mode"} $out/bin/agda-mode
       '';