Add utility GetInstance method to Json Asset refs in csharp

#2774

Source/Engine/Content/JsonAsset.cs

@@ -14,6 +14,17 @@ namespace FlaxEngine
         /// </summary>
         public object Instance => _instance ?? (_instance = CreateInstance());
 
+        /// <summary>
+        /// Gets the instance of the serialized object from the json data. Cached internally.
+        /// </summary>
+        /// <returns>The asset instance object or null.</returns>
+        public T GetInstance<T>()
+        {
+            if (Instance is T instance)
+                return instance;
+            return default;
+        }
+
         /// <summary>
         /// Creates a new instance of the serialized object from the json asset data.
         /// </summary>

Source/Engine/Content/JsonAssetReference.cs

@@ -33,6 +33,15 @@ namespace FlaxEngine
             Asset = asset;
         }
 
+        /// <summary>
+        /// Gets the deserialized native object instance of the given type. Returns null if asset is not loaded or loaded object has different type.
+        /// </summary>
+        /// <returns>The asset instance object or null.</returns>
+        public U GetInstance<U>()
+        {
+            return Asset ? Asset.GetInstance<U>() : default(U);
+        }
+
         /// <summary>
         /// Implicit cast operator.
         /// </summary>