Fix use of references to DD4hep handles
In DD4hep mode the DeXyz detector types are handles (kind of smart pointers) and they are usually temporary instances, so they should not be kept by reference, but copied otherwise one will get segfaults (like in Detector!368 (comment 6769177)). In DetDesc, instead, one should keep references to the DeXyz instances, that's why I added a helper with LHCb!3596 (merged), which I used here to fix the implementation of a few ToolBinder specializations.