KalmanVertexUpdator performance tuning for use in AMVF

This MR significantly speeds up the KalmanVertexUpdator's update method by replacing a temporarily created and subsequently destroyed xAOD::Vertex object by a slim struct. This is also done in the IVertexUpdator and propagated to all clients. This, together with local caching of a matrix inversion result, yields a factor of up to 4 speed improvement for the Adaptive multi vertex fitter (see https://its.cern.ch/jira/browse/ATLIDTRKCP-245).

In addition to this performance tuning, some clean-up to the code is performed (removal of commented lines, attempt to clean up indentation to a consistent scheme, uniform use of messaging macros, use of std algorithms where possible, fix of potential memory leak).

The changes were tested to not change the reco output (except for CPU/timings) compared to running the AMVF in an unchanged master.

Adding @sroe and @npetters who are also working on improving the AMVF performance.

Tracking/TrkVertexFitter/TrkVertexFitterUtils/src/KalmanVertexUpdator.cxx

@@ -55,12 +55,11 @@ namespace Trk{
  {
 
    //getting tracks at vertex
-   std::vector<Trk::VxTrackAtVertex>* tracksAtVertex( &vtx.vxTrackAtVertex() );
-   int tr_size = tracksAtVertex->size();
+   std::vector<Trk::VxTrackAtVertex> & tracksAtVertex = vtx.vxTrackAtVertex();
 
    //in case one wants to remove the track, one should be sure that this track
    //is already fitted to the vertex and the number of tracks at vertex is not 0
-   if( sign < 0 && tr_size == 0 )
+   if( sign < 0 && tracksAtVertex.size() == 0 )
    {
      msg(MSG::ERROR)  << "No tracks fitted to this vertex yet: can not remove any" << endmsg;
      msg(MSG::ERROR)  << "The copy of initial VxCandidate returned" << endmsg;
@@ -68,9 +67,9 @@ namespace Trk{
    }
 
    //trying to find requested track
-   auto righttrack = std::find(tracksAtVertex->begin(), tracksAtVertex->end(), trk); 
+   auto righttrack = std::find(tracksAtVertex.begin(), tracksAtVertex.end(), trk); 
 
-   if (righttrack == tracksAtVertex->end())
+   if (righttrack == tracksAtVertex.end())
    {
      ATH_MSG_VERBOSE ("The track requested for removal or adding is not found in the vector of tracks");
      if (sign<0) {
@@ -79,8 +78,8 @@ namespace Trk{
        return &vtx;
      }
 
-     tracksAtVertex->push_back( trk ); // tracksAtVertex stores the objects themselves in xAOD EDM and not pointers to them - this simply calls the copy constructor
-     righttrack = tracksAtVertex->end()-1; // vector::end() returns an iterator referring to the "past-the-end" element and thus does not point to any element!
+     tracksAtVertex.push_back( trk ); // tracksAtVertex stores the objects themselves in xAOD EDM and not pointers to them - this simply calls the copy constructor
+     righttrack = tracksAtVertex.end()-1; // vector::end() returns an iterator referring to the "past-the-end" element and thus does not point to any element!
      ATH_MSG_VERBOSE ("Updating vertex with new track which is still not attached to vertex. Adding it before updating...");
    }
 
@@ -116,7 +115,7 @@ namespace Trk{
 
    if( sign < 0 )
    {
-     tracksAtVertex->erase( righttrack );
+     tracksAtVertex.erase( righttrack );
    }
 
    return &vtx;