Reduce visibility of JSInstance (facebook#39738)

Summary:
Pull Request resolved: facebook#39738

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 JSInstance

Reviewed By: RSNara

Differential Revision: D49752139

fbshipit-source-id: cde2f37262d10f044d29968e67f619cb95648189

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

@@ -11,7 +11,7 @@
  * This interface includes the methods needed to use a running JS instance, without specifying any
  * of the bridge-specific initialization or lifecycle management.
  */
-public interface JSInstance {
+interface JSInstance {
   void invokeCallback(int callbackID, NativeArrayInterface arguments);
   // TODO if this interface survives refactoring, think about adding
   // callFunction.