[v25r0] Marlin Interface and workflow to include DD4hep Geometry, ILCDIRAC-659
This allows one to specify the DD4hep Detector Model the same way it is done in ddsim. Add DD4hepInit processor treatment in prepareXMLFile Refactor ddsim detectorXML code to Mixin classes so they can be shared between DDSim and Marlin
Add unittests for preparep[Marlin]XML File and refactor some of the prepareXMLFile code