Add isntance.id serialization support

src/Engine/babylon.engine.ts

@@ -566,7 +566,7 @@
         }
 
         public static get Version(): string {
-            return "3.1-rc-1";
+            return "3.1-rc-2";
         }
 
         // Updatable statics so stick with vars here

src/Mesh/babylon.mesh.ts

@@ -2174,6 +2174,7 @@
                 var instance = this.instances[index];
                 var serializationInstance: any = {
                     name: instance.name,
+                    id: instance.id,
                     position: instance.position.asArray(),
                     scaling: instance.scaling.asArray()
                 };
@@ -2473,7 +2474,6 @@
                 mesh.layerMask = 0x0FFFFFFF;
             }
 
-
             // Physics
             if (parsedMesh.physicsImpostor) {
                 mesh.physicsImpostor = new BABYLON.PhysicsImpostor(mesh, parsedMesh.physicsImpostor, {
@@ -2489,6 +2489,10 @@
                     var parsedInstance = parsedMesh.instances[index];
                     var instance = mesh.createInstance(parsedInstance.name);
 
+                    if (parsedInstance.id) {
+                        instance.id = parsedInstance.id;
+                    }
+
                     if (Tags) {
                         Tags.AddTagsTo(instance, parsedInstance.tags);
                     }