#1141 Replace workaround in PropertyDefinitionBuilder with virtual properties for varbase and vargroup (state: open)

FIXME: these are not properties yet, therefore we have to work around.

https://github.com/MetaModels/core/blob/8e61ba89a336e59996f5a5245370c2b8476efea5/src/MetaModels/DcGeneral/DefinitionBuilder/PropertyDefinitionBuilder.php#L90

When we have virtual properties, the following code should get re-added:

            $this->buildProperty(
                $definition,
                $metaModel->getAttribute('varbase'),
                $inputScreen->getProperty('varbase')['info']
            );
            $this->buildProperty(
                $definition,
                $metaModel->getAttribute('vargroup'),
                $inputScreen->getProperty('vargroup')['info']
            );