GeoPhysVol and GeoFullPhysVol Add() method is defined twice

GeoPhysVol and GeoFullPhysVol Add() method is defined twice: perhaps it could be moved to a base class?

• GeoPhysVol: https://gitlab.cern.ch/GeoModelDev/GeoModelCore/-/blob/3.1.2/GeoModelKernel/src/GeoPhysVol.cxx#L25

• GeoFullPhysVol: https://gitlab.cern.ch/GeoModelDev/GeoModelCore/-/blob/3.1.2/GeoModelKernel/src/GeoFullPhysVol.cxx#L26