rename root reference to agent game object

Project/Assets/ML-Agents/Examples/PushBlock/Scenes/PushBlockCollab.unity

   m_Modification:
     m_TransformParent: {fileID: 0}
     m_Modifications:
+    - target: {fileID: 4704531522807670703, guid: f5bbed44a6ea747a687fbbb738eb1730,
+        type: 3}
+      propertyPath: m_ShowGizmos
+      value: 0
+      objectReference: {fileID: 0}
     - target: {fileID: 8188317207052398481, guid: f5bbed44a6ea747a687fbbb738eb1730,
         type: 3}
       propertyPath: m_RootOrder

com.unity.ml-agents/Editor/GridSensorComponentEditor.cs

                 gridSize.vector3IntValue = new Vector3Int(newGridSize.x, 1, newGridSize.z);
             }
             EditorGUI.EndDisabledGroup();
-            EditorGUILayout.PropertyField(so.FindProperty(nameof(GridSensorComponent.m_RootReference)), true);
+            EditorGUILayout.PropertyField(so.FindProperty(nameof(GridSensorComponent.m_AgentGameObject)), true);
             EditorGUILayout.PropertyField(so.FindProperty(nameof(GridSensorComponent.m_RotateWithAgent)), true);
 
             EditorGUI.BeginDisabledGroup(!EditorUtilities.CanUpdateModelProperties());

com.unity.ml-agents/Runtime/Sensors/GridSensorComponent.cs

         }
 
         [HideInInspector, SerializeField]
-        internal GameObject m_RootReference;
+        internal GameObject m_AgentGameObject;
-        public GameObject RootReference
+        public GameObject AgentGameObject
-            get { return (m_RootReference == null ? gameObject : m_RootReference); }
-            set { m_RootReference = value; }
+            get { return (m_AgentGameObject == null ? gameObject : m_AgentGameObject); }
+            set { m_AgentGameObject = value; }
         }
 
         [HideInInspector, SerializeField]
                 m_RotateWithAgent,
                 m_ColliderMask,
                 gameObject,
-                RootReference,
+                AgentGameObject,
                 m_DetectableTags,
                 m_InitialColliderBufferSize,
                 m_MaxColliderBufferSize