flutter: optimize evaluation of appBuildDeps (#410782)

    let

      # https://discourse.nixos.org/t/handling-transitive-c-dependencies/5942/3

      deps =

        pkg:

        builtins.filter lib.isDerivation ((pkg.buildInputs or [ ]) ++ (pkg.propagatedBuildInputs or [ ]));

      collect = pkg: lib.unique ([ pkg ] ++ deps pkg ++ builtins.concatMap collect (deps pkg));

        pkg: lib.filter lib.isDerivation ((pkg.buildInputs or [ ]) ++ (pkg.propagatedBuildInputs or [ ]));

      withKey = pkg: {

        key = pkg.outPath;

        val = pkg;

      };

      collect = pkg: lib.map withKey ([ pkg ] ++ deps pkg);

    in

    builtins.concatMap collect appRuntimeDeps;

    lib.map (e: e.val) (

      lib.genericClosure {

        startSet = lib.map withKey appRuntimeDeps;

        operator = item: collect item.val;

      }

    );

  # Some header files and libraries are not properly located by the Flutter SDK.

  # They must be manually included.