Simplify serialisation of NativeJavaObject and JavaMembers

[aardvark179]

This fixes #2248. It turned out to be much simpler to fix than I had feared as almost everything was already serialisable.

[ZZZank]

A bit amazed by the fact that this PR didn't cause any additional error. I was expecting some NativeJavaField related errors since NativeJavaField is not serializable

[aardvark179]

Good point. I'll make that one serialisable too, and add some more to the tests.

[ZZZank]

I think serializing each NativeJavaXXX object separately is a bad idea, especially considering the raw member objects (Method, Field, etc) are not serializable, we will have to record their information and recreate the raw member manually, causing a huge amount of ''declaring class'' in serialized data.

Actually I think nothing in JavaMembers should be serializable at all, other than the name of the class that this JavaMembers reflects

[aardvark179]

We have to serialise those things, they can become reachable via multiple routes by assigning them to other variables.

I'd be happy to see a rewrite of JavaMembers that separates the raw members out and never serialises those, but then you'll have to make sure all the NativeJavaMethod/Constructor/etc stuff references things through that, and that none of those mutable JS objects are themselves stored inside JavaMembers