Adds fixes for react-native-windows UWP (#848)

Summary:
Specifically, updates the UWP .vcxproj for MSBuild and also exposes the UseLegacyStretchBehaviour API for use with react-native-windows.
Pull Request resolved: https://github.com/facebook/yoga/pull/848

Reviewed By: SidharthGuglani

Differential Revision: D13848609

Pulled By: davidaurelio

fbshipit-source-id: eab046ff3c47e49706f515e209d8aaf750c2198f

csharp/Facebook.Yoga/YogaValue.cs

@@ -91,17 +91,5 @@ namespace Facebook.Yoga
         {
             return Point(pointValue);
         }
-
-#if WINDOWS_UWP_ARM
-        internal static YogaValue MarshalValue(IntPtr ptr)
-        {
-            return Marshal.PtrToStructure<YogaValue>(ptr);
-        }
-#else
-        internal static YogaValue MarshalValue(YogaValue value)
-        {
-            return value;
-        }
-#endif
     }
 }