Apply react-native migration 0.62.2 -> 0.63.4

Summary:
In D25244631 (92bd68a371) we bumped the react-native dep of Flipper but we didn't apply the migration guide (sorry for missing that in the review), so the ReactNativeExample fell apart when trying to build for iOS. This diff applies the migration guide which nicely fixes that:

https://react-native-community.github.io/upgrade-helper/?from=0.62.2&to=0.63.4

Recreating the Podfile.lock and running `./gradlew clean` fixed all build problems after that.

Verified that `yarn ios` and `yarn android`, and building from XCode all work.

Found (probably unrelated / existing) issues:
* custom plugins only show up after initial app start after refreshing the plugin list by navigating to another diffs first, so this seems to be a UI staleness bug
* Network plugin doesn't seem to work ion iOS (either not showing traffic or not showing data at all)

Reviewed By: passy

Differential Revision: D25755490

fbshipit-source-id: baea8b152fb252deda04291ec197ab87c2fbe3eb

react-native/ReactNativeFlipperExample/ios/ReactNativeFlipperExample/AppDelegate.m

@@ -11,7 +11,7 @@
 #import <React/RCTBundleURLProvider.h>
 #import <React/RCTRootView.h>
 
-#if DEBUG
+#ifdef FB_SONARKIT_ENABLED
 #import <FlipperKit/FlipperClient.h>
 #import <FlipperKitLayoutPlugin/FlipperKitLayoutPlugin.h>
 #import <FlipperKitNetworkPlugin/FlipperKitNetworkPlugin.h>
@@ -38,7 +38,7 @@ static void InitializeFlipper(UIApplication* application) {
 
 - (BOOL)application:(UIApplication*)application
     didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
-#if DEBUG
+#ifdef FB_SONARKIT_ENABLED
   InitializeFlipper(application);
 #endif