Reorganize file structure by AdePT::Transport and AdePT:G4Integration libraries

[SeverinDiederichs]

Following #516, where AdePT was restructured into two libraries, this issue documents how to leverage the library split into a cleaner file tree:

The final file tree could look like this:

AdePT/
  include/
    AdePT/

     ### NOTE: core/AdePTConfiguration.hh and integration/AdePTTrackingManager.hh
     # are temporary to maintain backward compatibility with the user integration for a bit.
      core/
        AdePTConfiguration.hh              # temporary compatibility forwarding header
      integration/
        AdePTTrackingManager.hh             # temporary compatibility forwarding header
        G4EmStandardPhysics_AdePT.hh   # temporary compatibility forwarding header
        G4EmStandardPhysics_HepEm.hh # temporary compatibility forwarding header

     ### Actual structure starts here: ###

      g4integration/
        AdePTConfiguration.hh
        AdePTTrackingManager.hh

      transport/
        config/
          AdePTTransportConfig.hh

        support/
          Macros.h
          Global.h
          Portability.hh
          ResourceManagement.hh
          ResourceManagement.cuh
          PhysicalConstants.h
          SystemOfUnits.h
          AdePTPrecision.hh

        containers/
          Atomic.h
          BlockData.h
          MParray.h
          MParrayT.h
          SlotManager.cuh
          mpmc_bounded_queue.h
          VariableSizeObj.h
          VariableSizeObjAllocator.h

        random/
          Ranluxpp.h
          G4HepEmRandomEngineDeviceImpl.hh
          ranluxpp/
            helpers.h
            mulmod.h
            ranlux_lcg.h

        g4hepem/
          AdePTG4HepEmState.hh

        tracks/
          TrackData.h
          Track.cuh
          ParticleTypes.hh

        queues/
          TrackBuffer.hh
          ParticleQueues.cuh
          ParticleManager.cuh

        steps/
          GPUStep.hh
          HostCircularBuffer.hh
          DeviceStepBuffer.cuh
          GPUStepRecording.cuh
          GPUStepTransferManager.cuh

        geometry/
          GeometryAuxData.hh
          WDTData.hh

        state/
          EventState.hh
          GPUState.cuh
          TransportStats.hh
          DeviceGlobals.cuh

        navigation/
          AdePTNavigator.h
          BVHNavigator.h
          LoopNavigator.h
          SurfNavigator.h

        magneticfield/
          existing magnetic-field headers

        kernels/
          existing electron/gamma/WDT kernel headers

  src/
    transport/
      AdePTTransport.cc
      AdePTTransport.cu

      g4hepem/
        AdePTG4HepEmState.cpp

      steps/
        HostCircularBuffer.cpp

      # NOTE: the geometry.cu files and the gpu .cu files do not exist yet, this must be split, currently it is all in AsyncAdePTTransport.cuh
      geometry/
        GeometryUpload.cu
        WDTUpload.cu

      gpu/
        GPUInit.cu
        TransportLoop.cu
        TransportKernels.cu

    g4integration/
      config/
        AdePTConfiguration.cc
        AdePTConfigurationMessenger.cc

      tracking_managers/
        AdePTTrackingManager.cc
        AdePTThreadId.hh
        G4HepEmTrackingManagerSpecialized.cc

      geometry/
        AdePTGeometryBridge.cpp

      returned_steps/
        # Note: currently those are all in a single file AdePTGeant4Integration.cpp, this needs to be split
        AdePTGeant4Integration.cpp
        G4TouchableBuilder.cpp
        G4TrackBuilder.cpp
        G4StepBuilder.cpp
        DeferredStepReplay.cpp

      physics_constructors/
        G4EmStandardPhysics_AdePT.cc
        G4EmStandardPhysics_HepEm.cc

      cuda/
        G4IntegrationRdcFacade.cu

To obtain this structure, a few things are needed:

• Move the source files into the correct places (done in Move library sources into target folders #610)
• split the AsyncAdePTTransportStruct.cuh in clearer pieces (done in Split AsyncAdePTTransportStruct headers into topical headers #614)
• split the AsyncAdePTTransport.cuh in clearer pieces
• split the AdePTGeant4Integration in clearer pieces
• move the headers into the new structure. Keep a backward compatibility for a while (done in Move headers into transport and g4integration layout #612)
• Do same renaming: all the Async names should be deleted. (done in Remove Async from AdePTTransport naming #626)
• Further cleanup: the name spaces in AdePT are messy and not clearly ordered. That should be cleaned. E.g., the copcore name space can be deleted, there are various variations of AsyncAdePT namespaces etc.

Note that with this design copcore is going to be removed. In the current design of AdePT, there is no reason to keep a separate library, also it is not clear why e.g., the variablesizedobject lives in copcore but the atomics do not.