code: public SmartHandle convert(MethodType incoming) {
          return new SmartHandle(new Signature(incoming, signature.argNames()), handle.asType(incoming));
      }
docs: Create a new SmartHandle that converts arguments from the given type to
  the current signature's type, using the same argument names. This conversion
  is equivalent to MethodHandle#asType.
  
  @param incoming the target MethodType from which arguments will be converted
  @return a new SmartHandle that accepts the given argument types