code: public <T> Descriptor withMessageSerializer(Class<T> messageType, MessageSerializer<T, ?> messageSerializer) {
          return withMessageSerializer((Type) messageType, messageSerializer);
      }
docs: Provide a custom MessageSerializer for the given message type.
  
  @param messageType The type of the message.
  @param messageSerializer The message serializer for that type.
  @return A copy of this descriptor.