qtgraphicaleffects: Add dev output

This shrank my system closure by about 192 MiB.

pkgs/development/libraries/qt-5/modules/qtgraphicaleffects.nix

···
 qtModule {
   name = "qtgraphicaleffects";
   qtInputs = [ qtdeclarative ];
-  outputs = [ "out" ];
+  outputs = [ "out" "dev" ];
 }