Promote shadowColor to formsStackingContext property

Summary:
Changelog: [Internal]

View with `ShadowColor` was getting flattened and therefore views didn't have shadow property set.
This is fixed by promoting ShadowColor so in case it is set, it forms stacking context.

Reviewed By: shergin

Differential Revision: D20792201

fbshipit-source-id: 1033ac00e32047ffbb14e61b7c26348c578d132d

ReactCommon/fabric/components/view/ViewShadowNode.cpp

@@ -44,11 +44,11 @@ void ViewShadowNode::initialize() noexcept {
       !viewProps.nativeId.empty() || viewProps.accessible ||
       viewProps.opacity != 1.0 || viewProps.transform != Transform{} ||
       viewProps.zIndex != 0 || viewProps.getClipsContentToBounds() ||
-      viewProps.yogaStyle.positionType() == YGPositionTypeAbsolute;
+      viewProps.yogaStyle.positionType() == YGPositionTypeAbsolute ||
+      isColorMeaningful(viewProps.shadowColor);
 
   bool formsView = isColorMeaningful(viewProps.backgroundColor) ||
       isColorMeaningful(viewProps.foregroundColor) ||
-      isColorMeaningful(viewProps.shadowColor) ||
       !(viewProps.yogaStyle.border() == YGStyle::Edges{});
 
   formsView = formsView || formsStackingContext;