code: public static <K, V, V2> Lens.Simple<Map<K, V>, Map<K, V2>> mappingValues(Iso<V, V, V2, V2> iso) {
          return simpleLens(m -> toMap(HashMap::new, map(t -> t.biMapR(view(iso)), map(Tuple2::fromEntry, m.entrySet()))),
                            (s, b) -> view(mappingValues(iso.mirror()), b));
      }
docs: A lens that focuses on a map while mapping its values with the mapping {@link Iso}.
  <p>
  Note that for this lens to be lawful, <code>iso</code> must be lawful.
  
  @param iso  the mapping {@link Iso}
  @param <K>  the key type
  @param <V>  the unfocused map value type
  @param <V2> the focused map value type
  @return a lens that focuses on a map while mapping its values