[XABT] Separate marshal method storage from MarshalMethodClassifier to MarshalMethodsCollection.

[jpobst]

Today the marshal method scanning process is tightly coupled to scanning for JavaCallableWrappers. That is, when building CallableWrapperType objects, the MarshalMethodsClassifier is used to classify methods as marshal methods by calling ShouldBeDynamicallyRegistered (...).

However ShouldBeDynamicallyRegistered doesn't just return a simple bool, it has the side effect of building a list of MarshalMethodEntry objects that are used extensively throughout the build process.

We are likely going to need to build this list in places other than JavaCallableWrappers scanning: assembly rewriting will likely be before JCWs, and GenerateNativeMarshalMethodSources will likely be after JCWs.

As such:

• Rework MarshalMethodsClassifier to simply classify methods as LLVM marshal method eligible or not (dynamically registered).
• Move storage to a new MarshalMethodsCollection.

Future:

• We will likely need MarshalMethodsClassifier to also be able to detect marshal methods that have already been rewritten.