Fix resizeMode="cover" when image is resized

Since `RCTResizeModeCover` is implemented manually on macOS (iOS benefits from `UIViewContentModeScaleAspectFill` API), we need to reprocess the image any time the bounds of the view update. The `updateImage:` method was already called on resize, so this instead stores the original image in an ivar so it can call `RCTFillImagePreservingAspectRatio` from `updateImage:` instead.

Author: appden

Libraries/Image/RCTImageView.mm

@@ -128,6 +128,8 @@ @implementation RCTImageView
   // Whether the latest change of props requires the image to be reloaded
   BOOL _needsReload;
 
+  UIImage *_image; // TODO(macOS GH#774)
+
   RCTUIImageViewAnimated *_imageView;
 
 #if TARGET_OS_OSX // [TODO(macOS GH#774)
@@ -211,6 +213,10 @@ - (void)updateWithImage:(UIImage *)image
 #else // [TODO(macOS GH#774)
     image.capInsets = _capInsets;
     image.resizingMode = NSImageResizingModeTile;
+  } else if (_resizeMode == RCTResizeModeCover) {
+    if (!NSEqualSizes(self.bounds.size, NSZeroSize)) {
+      image = RCTFillImagePreservingAspectRatio(image, self.bounds.size, self.window.backingScaleFactor ?: 1.0);
+    }
 #endif // ]TODO(macOS GH#774)
   } else if (!UIEdgeInsetsEqualToEdgeInsets(UIEdgeInsetsZero, _capInsets)) {
     // Applying capInsets of 0 will switch the "resizingMode" of the image to "tile" which is undesired
@@ -233,17 +239,13 @@ - (void)setImage:(UIImage *)image
 {
   image = image ?: _defaultImage;
   if (image != self.image) {
-#if TARGET_OS_OSX // [TODO(macOS GH#774)
-    if (image && _resizeMode == RCTResizeModeCover && !NSEqualSizes(self.bounds.size, NSZeroSize)) {
-      image = RCTFillImagePreservingAspectRatio(image, self.bounds.size, self.window.backingScaleFactor ?: 1.0);
-    }
-#endif // ]TODO(macOS GH#774)
+    _image = image; // TODO(macOS GH#774)
     [self updateWithImage:image];
   }
 }
 
 - (UIImage *)image {
-  return _imageView.image;
+  return _image ?: _imageView.image; // TODO(macOS GH#774)
 }
 
 - (void)setBlurRadius:(CGFloat)blurRadius