Reduce visibility of ProgressiveStringDecoder

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 ProgressiveStringDecoder

Reviewed By: arushikesarwani94

Differential Revision: D49803293

fbshipit-source-id: 93d28f579d51e220c46e74d264f84c5dce743e72

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/modules/network/ProgressiveStringDecoder.java

@@ -23,7 +23,7 @@
  * <p>This class is designed in assumption that original byte stream is correctly formatted string
  * in given encoding. Otherwise some parts of the data won't be decoded.
  */
-public class ProgressiveStringDecoder {
+class ProgressiveStringDecoder {
 
   private static final String EMPTY_STRING = "";