[core.room] fix binding validation to check inherited external end ports

Issue 46 is partly an awkward interaction between the diagram editor behavior and the core room xtext services. The diagram editor uses the xtext validator directly on combinations of EObjects that would normally not be possible in an xtext document (due to scope provider constraints). This means that the validator has to account for cases that are outside the possible xtext scope.

Not sure if this should be refactored in some way, or if it's worth it?

Commit message: Validation for connection of external end ports now also accounts for inherited ports. Note that due to current scope provider behavior, it is not actually possible in the textual editor to encounter this case. HOWEVER, it does become an issue in the diagram editor, because it currently uses ValidationUtil on arbitrary ports in the diagram without consulting the scope.

Issue #46 (closed)

Closes #46 (closed)

Edited by Eyrak Paen-Rochlitz

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