Added glTF sheen and clear coat validation tests

tests/validation/config.json

@@ -599,6 +599,16 @@
             "referenceImage": "gltfTextureSampler1.png"
         },
         {
+            "title": "GLTF Sheen",
+            "playgroundId": "#YG3BBF#2",
+            "referenceImage": "glTFSheen.png"
+        },
+        {
+            "title": "GLTF ClearCoat",
+            "playgroundId": "#YG3BBF#1",
+            "referenceImage": "glTFClearCoat.png"
+        },
+        {
             "title": "GLTF Serializer with Negative World Matrix",
             "playgroundId": "#KX53VK#35",
             "referenceImage": "glTFSerializerNegativeWorldMatrix.png",