java.lang.reflect.Parameter#isSynthetic() should not depend on user option for enum constructors

Our JEP 118 implementation added synthetic flags to the parameters of enum's private constructor to be stored in class files. But this depends on an user option, which makes sense for parameter names. But since have an API that depends on this implementation, it will be good to store the synthetic information for enum constructors by default, just as we do for records.