UCM12 — fix problems in the XMI file of the UCM metamodel

This issue corresponds to remarks from Pete Rivett regarding the XMI file of the UML metamodel.

The namespace for UML is wrong xmlns:uml="http://www.eclipse.org/uml2/5.0.0/UML"

Remove xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore"
And all eAnnotations (8)

The package URI should conform to OMG’s standard URI="http://org.omg.ucm/1.0/metamodels/base/commons".
It should be https://www.omg.org/spec/UCM/20190501/ucm_base.uml

Since it’s a metamodel the topmost element should be the Package not the uml:Model

The primitive types do not reference the standard ones:
For example
<type xmi:type="uml:PrimitiveType" href="pathmap://UML_LIBRARIES/UMLPrimitiveTypes.library.uml#String"/>

The URI should be
https://www.omg.org/spec/UCM/20190501/ucm_base.uml

There should be no xmi:type or reference elements such as the above.
There should be no xmi:version.

fix conformity issues in the XMI metamodel file

Fixed the problems the issue points out.