Use iOS 13 dark content status bar style

Author: jayjun

shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.mm

@@ -171,12 +171,17 @@ - (void)setSystemChromeSystemUIOverlayStyle:(NSDictionary*)message {
     return;
 
   UIStatusBarStyle statusBarStyle;
-  if ([style isEqualToString:@"Brightness.dark"])
+  if ([style isEqualToString:@"Brightness.dark"]) {
     statusBarStyle = UIStatusBarStyleLightContent;
-  else if ([style isEqualToString:@"Brightness.light"])
-    statusBarStyle = UIStatusBarStyleDefault;
-  else
+  } else if ([style isEqualToString:@"Brightness.light"]) {
+    if (@available(iOS 13, *)) {
+      statusBarStyle = UIStatusBarStyleDarkContent;
+    } else {
+      statusBarStyle = UIStatusBarStyleDefault;
+    }
+  } else {
     return;
+  }
 
   NSNumber* infoValue = [[NSBundle mainBundle]
       objectForInfoDictionaryKey:@"UIViewControllerBasedStatusBarAppearance"];