rn-demo-app: Implement getModuleInstanceFromClass:

Summary:
While not strictly necessary for rn-demo-app at this point, we do need to provide the `getModuleInstanceFromClass:` implementation to simplify the TurboModule migration process later on.

Also, removed some issues in the Xcode project that must have been introduced during a recent rebase (duplicate Embed Pods build phases).

Changelog: [Internal]

Reviewed By: fkgozali

Differential Revision: D30618992

fbshipit-source-id: a9b496cfa0cd34fca6389ddf829613aa13ea409d

packages/rn-tester/RNTester/AppDelegate.mm

@@ -206,6 +206,7 @@ - (Class)getModuleClassFromName:(const char *)name
 
 - (id<RCTTurboModule>)getModuleInstanceFromClass:(Class)moduleClass
 {
+  // Set up the default RCTImageLoader and RCTNetworking modules.
   if (moduleClass == RCTImageLoader.class) {
     return [[moduleClass alloc] initWithRedirectDelegate:nil
         loadersProvider:^NSArray<id<RCTImageURLLoader>> *(RCTModuleRegistry * moduleRegistry) {