Fabric: Proper background color setting for RCTViewComponentView

Summary: Setting value directly to ivar makes impossible to subclasses to react of this; this is a bug.

Reviewed By: mdvacca

Differential Revision: D15776691

fbshipit-source-id: 10f9be975ee673b2db46c24ba41b18f6d6ddf0a3

React/Fabric/Mounting/ComponentViews/View/RCTViewComponentView.mm

@@ -120,7 +120,7 @@ using namespace facebook::react;
 
   // `backgroundColor`
   if (oldViewProps.backgroundColor != newViewProps.backgroundColor) {
-    _backgroundColor = RCTUIColorFromSharedColor(newViewProps.backgroundColor);
+    self.backgroundColor = RCTUIColorFromSharedColor(newViewProps.backgroundColor);
     needsInvalidateLayer = YES;
   }