[BUG] Support anonymous Characteristics and Constraints

[atextor]

How: List of performed steps

Try to load an Aspect Model with an anonymous Characteristic, e.g.,

@prefix samm: <urn:samm:org.eclipse.esmf.samm:meta-model:2.2.0#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix : <urn:samm:com.examples:1.0.0#> .

:AspectWithAnon a samm:Aspect ;
   samm:properties ( :property1 ) ;
   samm:operations ( ) ;
   samm:events ( ) .

:property1 a samm:Property ;
   samm:characteristic [
      a samm:Characteristic ;
      samm:dataType xsd:string ;
   ] .

What: Actual result vs expected result
Expected: Model is loaded and can be edited
Actual: Loading fails. It's also not possible to manually create an unnamed Characteristic in the context of a Property.

Where: (e.g. component, version, url, your system info)
AME 5.6.1