Prevent overlap between DeadMaterial and FWDBeamLine G4PhysicsRegions (ATLASSIM-6132)
This enables the ForwardTransportModel G4VFastSimulationModel to be used when ALFA/AFP/ZDC, but not the FwdRegion are activated.
Fix ForwardTransportModel logic to be compatible with HepMC3 and modern Geant4 versions and remove thread calls to ForwardTransportSvc.
ForwardTransportSvc should be cleaned up in a follow up merge request.
Edited by John Derek Chapman