Reduce visibility of YogaNodePool

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 YogaNodePool

Reviewed By: arushikesarwani94

Differential Revision: D49803281

fbshipit-source-id: 092826dcd4b7c9858240b760e87eb87a32e54a25

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

@@ -11,7 +11,7 @@
 import com.facebook.yoga.YogaNode;
 
 /** Static holder for a recycling pool of YogaNodes. */
-public class YogaNodePool {
+class YogaNodePool {
 
   private static final Object sInitLock = new Object();
   private static ClearableSynchronizedPool<YogaNode> sPool;