Fix new arch message serialization by adding 'isMainFrame' property to the data structure in iOS implementation.

Author: tian000

apple/RNCWebView.mm

@@ -134,7 +134,8 @@ - (instancetype)initWithFrame:(CGRect)frame
                     .canGoBack = static_cast<bool>([[dictionary valueForKey:@"canGoBack"] boolValue]),
                     .canGoForward = static_cast<bool>([[dictionary valueForKey:@"canGoForward"] boolValue]),
                     .loading = static_cast<bool>([[dictionary valueForKey:@"loading"] boolValue]),
-                    .data = std::string([[dictionary valueForKey:@"data"] UTF8String])
+                    .data = std::string([[dictionary valueForKey:@"data"] UTF8String]),
+                    .isMainFrame = static_cast<bool>([[dictionary valueForKey:@"isMainFrame"] boolValue])
                 };
                 webViewEventEmitter->onMessage(data);
             }