simplify serialization of MemberBox

[ZZZank]

1. There's a boolean at the start of serialized data, representing whether the member is present. This PR removed this because MemberBox is an internal class and never has its member set to null
2. The writing/reading of parameter types is rewritten to read/write method descriptor string, which can be converted from/to parameter types array via MethodType.
3. serialVersionUID updated to reflect serialization logic change