DD4hep integration requires a number of small interface changes, e.g. avoiding Gaudi and DetDesc specific types. It also requires conditions to be dealt with via the functional framework.
This MR is preparing the DD4hep implementation by implementing those changes and modernizing a bit the code on the way
Part of a set of MRs : !3309 (merged) Lbcom!588 (merged) Rec!2607 (merged) Boole!368 (merged) Allen!704 (merged) Panoramix!112 (merged) Alignment!222 (merged)