Reduce visibility of VelocityHelper

Summary:
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.

bypass-github-export-checks

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

Reviewed By: arushikesarwani94

Differential Revision: D49803269

fbshipit-source-id: 6b9dcf39979c8b4da5f736ba4fce3d495245755d

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/VelocityHelper.java

@@ -15,7 +15,7 @@
  * This Class helps to calculate the velocity for all ScrollView. The x and y velocity will later on
  * send to ReactScrollViewHelper for further use.
  */
-public class VelocityHelper {
+class VelocityHelper {
 
   private @Nullable VelocityTracker mVelocityTracker;
   private float mXVelocity;