qt6.qttools: symlink bin to dev output

There are several reference to "${qttools.dev}/bin" treewide, adding the
symlink to fix compatibility with these packages.

pkgs/development/libraries/qt-6/modules/qttools.nix

@@ -41,4 +41,8 @@ qtModule {
     "bin/macdeployqt"
   ];
 
+  postInstall = ''
+    mkdir -p "$dev"
+    ln -s "$out/bin" "$dev/bin"
+  '';
 }