As preparations to use the Diagram ModelData further isolate
it from the oox-library-only drawingML Shape used for import.
It is necessary to completely isolate the Diagram ModelData
from the Diagram import mechanism as a preparation to be
able to re-create that Shapes on-demand anytime if needed
for re-layout(s).
Also removed one unused loadDiagram implementation and
streamlined the AdvancedDiagramHelper some more.
Change-Id: I7a7c55389e0d00f70c02db73ce2c3ff9ce7a5b22
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/132058
Tested-by: Jenkins
Reviewed-by: Armin Le Grand <Armin.Le.Grand@me.com>
b658fdc335