Reduce visibility of ReactPackageHelper (#39728)

Summary:
Pull Request resolved: #39728

In an attempt to reduce footprint of React Native Android public APIs we are reducing visibility of classes and interfaces that are not meant to be used publicly OR are public but have no usages.
As part of our analysis, which involved looking for usages inside the Meta codebase and code search in OSS, we've detected that this class/interface is public but it's not used from other packages.

If you are using this class or interface please comment in this PR and we will restate the public access.

changelog: [Android][Changed] Reducing visibility of ReactPackageHelper

Reviewed By: RSNara

Differential Revision: D49752142

fbshipit-source-id: d21812609a946faf2f9183993f28192dda34e132

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactPackageHelper.java

@@ -16,7 +16,7 @@
 import java.util.Iterator;
 import java.util.List;
 
-public class ReactPackageHelper {
+class ReactPackageHelper {
   /**
    * A helper method to iterate over a list of Native Modules and convert them to an iterable.
    *