Identify Dummy Types in UML

[SofiaAnanieva]

This issue directly follows issue 167. We assume that external types in Java have been successfully propagated to UML as dummy types. These external types must be ignored when propagating in the other direction from UML to Java in order to ensure that propagation from UML to Java is not corrupted by propagating such types transitively back to Java.

As discussed in the latests Vitruv ConCall (October 28, 2021), possible solutions could be to i) mark the dummy types with a respective tag to identify such external types, or to ii) match each type with the Java class library (or other external libraries) to identify them as external types and ignore them during propagation from UML to Java.