ParticleJetTools: Use Accessor, etc instead of auxdata().

Replace auxdata, etc. with Accessor classes.
Moving to deprecate these usages in the Athena build.

PhysicsAnalysis/AnalysisCommon/ParticleJetTools/Root/JetParticleCenterOfMassAssociation.cxx

 /*
-  Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 */
 
 // author: jie.yu@cern.ch
 
 #include "ParticleJetTools/JetParticleCenterOfMassAssociation.h"
 #include "AsgMessaging/Check.h"
+#include "AthContainers/ConstAccessor.h"
 #include "TLorentzVector.h"
 
 using namespace std;
@@ -35,17 +36,18 @@ JetParticleCenterOfMassAssociation::match(const JetContainer& jets, const xAOD::
 
         const IParticle& part = **part_itr;
 
+        static const SG::ConstAccessor< ElementLink< JetContainer > > ParentAcc ("Parent");
         double deltaAngleMatch = 999.;
         int matchjetidx = -1;
         for (unsigned int iJet = 0; iJet < jets.size(); iJet++) {
             const Jet& jet = *jets[iJet];
 
-            bool foundEL = jet.isAvailable< ElementLink< JetContainer > >("Parent");
+            bool foundEL = ParentAcc.isAvailable (jet);
             if ( ! foundEL ){
                 ATH_MSG_WARNING("PARTICLE to JET center-of-mass Associator: PARENT jet not available.");
                 continue;
             }
-            ElementLink< JetContainer > assoParentJet = jet.auxdata< ElementLink< JetContainer > >("Parent");
+            ElementLink< JetContainer > assoParentJet = ParentAcc (jet);
             if ( ! assoParentJet.isValid()){
                 ATH_MSG_WARNING("PARTICLE to JET center-of-mass Associator: Unable to get parent link Null ptr is returned.");
                 continue;

PhysicsAnalysis/AnalysisCommon/ParticleJetTools/Root/JetTruthLabelingTool.cxx

 /*
-   Copyright (C) 2002-2023 CERN for the benefit of the ATLAS collaboration
+   Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 */
 
 #include "ParticleJetTools/JetTruthLabelingTool.h"
@@ -8,6 +8,7 @@
 #include "AsgDataHandles/ReadDecorHandle.h"
 #include "AsgDataHandles/WriteDecorHandle.h"
 #include "AsgTools/CurrentContext.h"
+#include "AthContainers/ConstAccessor.h"
 
 JetTruthLabelingTool::JetTruthLabelingTool(const std::string& name) :
   asg::AsgTool(name)
@@ -326,12 +327,13 @@ StatusCode JetTruthLabelingTool::labelRecoJets(DecorHandles& dh,
     truthGroomedJets = SG::makeHandle(m_truthGroomedJetCollectionName, ctx);
   }
   const SG::AuxElement::Accessor<int> nbAcc (m_truthLabelName + "_NB");
+  static const SG::ConstAccessor< ElementLink< xAOD::JetContainer > > ParentAcc ("Parent");
   for(const xAOD::Jet *jet : jets) {
 
     /// Get parent ungroomed reco jet for matching
     const xAOD::Jet* parent = nullptr;
     if ( m_matchUngroomedParent ){
-      ElementLink<xAOD::JetContainer> element_link = jet->auxdata<ElementLink<xAOD::JetContainer> >("Parent");
+      ElementLink<xAOD::JetContainer> element_link = ParentAcc (*jet);
       if ( element_link.isValid() ) {
         parent = *element_link;
       }
@@ -405,7 +407,7 @@ StatusCode JetTruthLabelingTool::labelRecoJets(DecorHandles& dh,
     if ( m_getTruthGroomedJetValues ) {
       if ( matchTruthJet ) {
         for ( const xAOD::Jet* truthGroomedJet : *truthGroomedJets ) {
-          ElementLink<xAOD::JetContainer> element_link = truthGroomedJet->auxdata<ElementLink<xAOD::JetContainer> >("Parent");
+          ElementLink<xAOD::JetContainer> element_link = ParentAcc (*truthGroomedJet);
           if ( !element_link.isValid() ) { continue; }
           if ( matchTruthJet == *element_link ) {
             matchTruthGroomedJet = truthGroomedJet;