Use main.jsbundle in iOS template for production build (#22531)

Summary:
Default HelloWorld template for iOS doesn't make production main.jsbundle. This is little bit confusing in compare with Android building app when everything works one first run.

Make it seamless, reduce confuse.
Based on docs https://facebook.github.io/react-native/docs/running-on-device#3-configure-app-to-use-static-bundle

Fixes #22335
Fixes #18562
Pull Request resolved: #22531

Differential Revision: D13372773

Pulled By: cpojer

fbshipit-source-id: 888c675b7d11b1a323445e092ec9ff83924c42f4

local-cli/templates/HelloWorld/ios/HelloWorld/AppDelegate.m

@@ -16,7 +16,11 @@ - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(
 {
   NSURL *jsCodeLocation;
 
-  jsCodeLocation = [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index" fallbackResource:nil];
+  #ifdef DEBUG
+    jsCodeLocation = [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index" fallbackResource:nil];
+  #else
+    jsCodeLocation = [[NSBundle mainBundle] URLForResource:@"main" withExtension:@"jsbundle"];
+  #endif
 
   RCTRootView *rootView = [[RCTRootView alloc] initWithBundleURL:jsCodeLocation
                                                       moduleName:@"HelloWorld"