Fix C++ prop type for the Image.defaultSource

Summary:
`defaultSource` is defined as a single `ImageSource` in docs (https://reactnative.dev/docs/next/image#defaultsource) but its type is a vector of `ImageSource`s in `ImageProps.h`.

This diff changes its C++ type to just `ImageSource`.

Technically, this is a breaking change, however I don't think folks should directly access `ImageProps` outside of `RCTImageComponentView.mm`
Moreover, this prop is actually not implemented in Fabric, so this change should have no practical effect.

Changelog: [Internal]

Facebook
T208171435 - [RN][Fabric][iOS] Implement defaultSource support for Image

Differential Revision: D65821570

packages/react-native/ReactCommon/react/renderer/components/image/ImageProps.cpp

@@ -26,14 +26,14 @@ ImageProps::ImageProps(
                     "source",
                     sourceProps.sources,
                     {})),
-      defaultSources(
+      defaultSource(
           ReactNativeFeatureFlags::enableCppPropsIteratorSetter()
-              ? sourceProps.defaultSources
+              ? sourceProps.defaultSource
               : convertRawProp(
                     context,
                     rawProps,
                     "defaultSource",
-                    sourceProps.defaultSources,
+                    sourceProps.defaultSource,
                     {})),
       resizeMode(
           ReactNativeFeatureFlags::enableCppPropsIteratorSetter()
@@ -95,7 +95,7 @@ void ImageProps::setProp(
 
   switch (hash) {
     RAW_SET_PROP_SWITCH_CASE(sources, "source");
-    RAW_SET_PROP_SWITCH_CASE(defaultSources, "defaultSource");
+    RAW_SET_PROP_SWITCH_CASE(defaultSource, "defaultSource");
     RAW_SET_PROP_SWITCH_CASE_BASIC(resizeMode);
     RAW_SET_PROP_SWITCH_CASE_BASIC(blurRadius);
     RAW_SET_PROP_SWITCH_CASE_BASIC(capInsets);

packages/react-native/ReactCommon/react/renderer/components/image/ImageProps.h

@@ -32,7 +32,7 @@ class ImageProps final : public ViewProps {
 #pragma mark - Props
 
   ImageSources sources{};
-  ImageSources defaultSources{};
+  ImageSource defaultSource{};
   ImageResizeMode resizeMode{ImageResizeMode::Stretch};
   Float blurRadius{};
   EdgeInsets capInsets{};