ModelStateHelper doesn't support RTD distributed in several emf resources

[dvojtise]

Currently, when looking for RTD to save, the generated ModelStateHelper searches only in the current root model element contents.

(cf. https://github.com/eclipse/gemoc-studio-execution-moccml/blob/945a7f37aa1575494e8e2de636030320f60fe6f1/examples/moccmlTFSM/language_workbench/org.eclipse.gemoc.example.moccml.tfsm/xdsml-java-gen/oncurrenttfsm/xdsml/api/impl/OncurrentTFSMModelStateHelper.java#L47 )

In the case of complex models split into several resources, the ModelStateHelper will ignore RTD that not directly contained by this root model element.

I suggest to use a crossreferencer in order to look for all resources used by the model.