Provide extensible scope for named references in StoEx parser and editor
After COMMONS-27, named references can be implemented in a type safe way. In order to make this work, the scope of the Xtext parser has to contain the available model elements provided by other models. There must not be a dependency from StoEx to the implementing meta models. Therefore, there has to be an extension point to contribute scopes. In addition, the Xtext grammar has to be adjusted to support such cross references.
Steps for realization:
Adjust Xtext grammar to the changed named reference class
Create an extension point for contributing scope implementations
Adjust existing scoping to consider the extensions
Test implementation with example provider for scoping (PCM)