SModel: drop canFireEvent/canFireReadEvent() from SModelInternal as there's no need to expose these implementation-specific methods to implementation classes via an interface.
SModelOperations: drop duplicated validateLanguagesAndImports method
SModelOperations: do not duplicate code in ModelDependencyManager and in SModelOperations, drop deprecated methods
SModelOperations: methods specific to particular cases (not eligible to 'internal-api' exposure) moved closer to their usage sites.
SModelOperations: do not re-resolve accessory models
SModel: fix node read test - method signature had changed