Summary:
On an iPhone running iOS 10.3.3, I'm not seeing the UIContentSizeCategoryDidChangeNotification fire when changing the system's font scale setting. Registering for the event on `nil` instead of on the application object fixes the issue.
**Test Plan**
Verified that text in an RN app changes size when you change the system's font scale setting (Settings -> General -> Accessibility -> Larger Text). By default, RN text is supposed to scale with the system setting.
Adam Comella
Microsoft Corp.
Closes https://github.com/facebook/react-native/pull/15522
Differential Revision: D5657449
Pulled By: shergin
fbshipit-source-id: d7a6a730c5cd6eb3833274a1f2029663ad3a7ad2
2b7cb46ddb