WIP: De classes for UT geometry

patch generated by https://gitlab.cern.ch/lhcb/Detector/-/jobs/12556279

@xuyuan where are we with this development ? May I take it over to make it at least compile and integrate it into master ? We are trying to have fully compiling DD4hep setup in master and UT is one of the very few remaining cases.

If you're ok for me to take it over, please submit the latest state of what you have so that we do not loose anything of your work !

mentioned in merge request !144 (merged)

This has been superseeded by !144 (merged), so closing it

closed