fix(ImageLoader): getSize API behavior for local assets (microsoft#935)

Recent changes to the ReactImageManager and the ImageLoaderModule introduced a bug where local assets were not behaving correctly because they did not work with the ImageCache API from UWP Community Toolkit.  This fix works around that limitation and uses the previous `getSize` implementation approach for non-HTTP assets.

Fixes microsoft#930

Author: rozele

ReactWindows/ReactNative/Modules/Image/ImageLoaderModule.cs

@@ -2,6 +2,8 @@
 using Newtonsoft.Json.Linq;
 using ReactNative.Bridge;
 using System;
+using System.Reactive.Linq;
+using Windows.UI.Xaml.Media.Imaging;
 
 namespace ReactNative.Modules.Image
 {
@@ -57,12 +59,39 @@ public void getSize(string uriString, IPromise promise)
             {
                 try
                 {
-                    var bitmapImage = await ImageCache.Instance.GetFromCacheAsync(new Uri(uriString), true);
-                    promise.Resolve(new JObject
+                    if (BitmapImageHelpers.IsHttpUri(uriString))
                     {
-                        { "width", bitmapImage.PixelWidth },
-                        { "height", bitmapImage.PixelHeight },
-                    });
+                        var bitmapImage = await ImageCache.Instance.GetFromCacheAsync(new Uri(uriString), true);
+                        promise.Resolve(new JObject
+                        {
+                            { "width", bitmapImage.PixelWidth },
+                            { "height", bitmapImage.PixelHeight },
+                        });
+                    }
+                    else
+                    {
+                        var bitmapImage = new BitmapImage();
+                        var loadQuery = bitmapImage.GetStreamLoadObservable()
+                            .Where(status => status.LoadStatus == ImageLoadStatus.OnLoadEnd)
+                            .FirstAsync()
+                            .Replay(1);
+
+                        using (loadQuery.Connect())
+                        {
+                            using (var stream = await BitmapImageHelpers.GetStreamAsync(uriString))
+                            {
+                                await bitmapImage.SetSourceAsync(stream);
+                            }
+
+                            await loadQuery;
+
+                            promise.Resolve(new JObject
+                            {
+                                { "width", bitmapImage.PixelWidth },
+                                { "height", bitmapImage.PixelHeight },
+                            });
+                        }
+                    }
                 }
                 catch (Exception ex)
                 {