ST6RI-912 Eliminate adding of "nonunique" property to metamodel

[seidewitz]

This PR revises the Xtext grammars for KerML and SysML so that it is no longer to add the property Feature::isNonunique to the Ecore metamodel.

Background

The default for the Feature::isUnique property is true. In the textual notation, the nonunique keyword is used to set this property to false. However, the Xtext grammar ?= notation only supports setting a property to true on the parsing of a specific keyword.

The previous workaround for this was for the CustomUML2EcoreConverter toadd an isNonunique property to Feature when generating the Ecore metamodel. The setting of this property was implemented to set isUnique to the opposite value. This allowed isNonunique ?= 'nonunique' to be used in the Xtext grammar.

Changes

1. In each of the KerML and SysML Xtext grammars:
   • Add the production:

     Nonunique returns Ecore::EBoolean :
         'nonunique'
     ;
     

   • Change isNonunique ?= 'nonunique' to isUnique = Nonunique.
2. Add package org.omg.kerml.xtext.conversion, with the Xtend classes:
   • KerMLValueConverterService – This is bound as the IValueConverterService in KerMLRuntimeModule.
   • NonuniqueValueConverter – This is the single provided value converter. It converts the value "nonunique" to false.
3. Remove isNonunique property.
   • Update org.omg.sysml.importer.CustomUML2EcoreImporter to not add isNonunique to Feature.
   • Remove Feature_isNonunique_SettingDelegate.
   • Regenerate SysML.ecore and org.omg.sysml.lang.sysml.Feature.