Switched over to newtonsoft json so we can properly write out skeleton info

com.unity.perception/Runtime/GroundTruth/Exporters/Coco/CocoExporter.cs

                     }
                 }
 
+#if false
+#else
+                var builder = new StringBuilder();
+                var sw = new StringWriter(builder);
+
+                var serializer = new JsonSerializer();
+
+                using (var writer = new JsonTextWriter(sw))
+                {
+                    serializer.Serialize(writer, merged);
+                }
+
+                var json = builder.ToString();
+#endif
                 m_KeypointCategoryWritingTask = m_KeypointCategoryStream.WriteAsync(json);
             }
         }
                         else
                             keypointJson += ",";
 
-                        keypointJson += JsonUtility.ToJson(kp);
+                        var builder = new StringBuilder();
+                        var stringWriter = new StringWriter(builder);
+
+                        var serializer = new JsonSerializer();
+
+                        using (var writer = new JsonTextWriter(stringWriter))
+                        {
+                            serializer.Serialize(writer, kp);
+                        }
+
+                        keypointJson += builder.ToString();
+
                     }
                 }
             }

com.unity.perception/Runtime/GroundTruth/Exporters/Coco/CocoTypes.cs

 using System;
 using System.Collections.Generic;
+using Newtonsoft.Json;
 
 namespace UnityEngine.Perception.GroundTruth.Exporters.Coco
 {
         [Serializable]
         public class ObjectDetectionAnnotation
         {
+            [JsonProperty(Order = -2)]
+            [JsonProperty(Order = -2)]
+            [JsonProperty(Order = -2)]
+            [JsonProperty(Order = -2)]
+            [JsonProperty(Order = -2)]
+            [JsonProperty(Order = -2)]
+            [JsonProperty(Order = -2)]
             public int iscrowd;
 
             public static ObjectDetectionAnnotation FromBoundingBoxValue(BoundingBox2DLabeler.BoundingBoxValue bbox)
         [Serializable]
         public class ObjectDetectionCategory
         {
+            [JsonProperty(Order = -2)]
-            public string name;
-            public string supercategory;
+            [JsonProperty(Order = -2)]
+            public string name = string.Empty;
+            [JsonProperty(Order = -2)]
+            public string supercategory = string.Empty;
         }
 
         [Serializable]
 
         public class KeypointAnnotation : ObjectDetectionAnnotation
         {
+            public int num_keypoints;
-            public int num_keypoints;
+
 
             public void CopyObjectDetectionData(ObjectDetectionAnnotation objDetection)
             {