This MR align the content of the LHCb Geant4 project with that of the official Geant4 repository, with the addition of LHCb patches, physics lists and tests.
The Geant4 version used as baseline is tag lhcb/v106r2p5 from https://gitlab.cern.ch/lhcb/Geant4-srcs
Note This MR replaces !78 (closed) (see !78 (comment 5039250))
do not squash the commits in this MR as they are meant to pull original Geant4 history into this repository.
