Adds fixes for react-native-windows UWP

Specifically, updates the UWP .vcxproj for MSBuild and also exposes the UseLegacyStretchBehaviour API for use with react-native-windows.

csharp/Facebook.Yoga/YogaConfig.cs

@@ -1,4 +1,4 @@
-/**
+/**
  * Copyright (c) Facebook, Inc. and its affiliates.
  *
  * This source code is licensed under the MIT license found in the
@@ -117,6 +117,19 @@ namespace Facebook.Yoga
             }
         }
 
+        public bool UseLegacyStretchBehaviour
+        {
+            get
+            {
+                return Native.YGConfigGetUseLegacyStretchBehaviour(_ygConfig);
+            }
+
+            set
+            {
+                Native.YGConfigSetUseLegacyStretchBehaviour(_ygConfig, value);
+            }
+        }
+
         public float PointScaleFactor
         {
             set