Make ForwardingStandardJavaFileManager public.

RELNOTES=Make `ForwardingStandardJavaFileManager` public.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=223862220

src/main/java/com/google/testing/compile/ForwardingStandardJavaFileManager.java

@@ -30,15 +30,15 @@
  * Forwards calls to a given {@link StandardJavaFileManager}. Subclasses of this class might
  * override some of these methods and might also provide additional fields and methods.
  */
-class ForwardingStandardJavaFileManager extends ForwardingJavaFileManager<StandardJavaFileManager>
-    implements StandardJavaFileManager {
+public class ForwardingStandardJavaFileManager
+    extends ForwardingJavaFileManager<StandardJavaFileManager> implements StandardJavaFileManager {
 
   /**
    * Creates a new instance of ForwardingStandardJavaFileManager.
    *
    * @param fileManager delegate to this file manager
    */
-  ForwardingStandardJavaFileManager(StandardJavaFileManager fileManager) {
+  protected ForwardingStandardJavaFileManager(StandardJavaFileManager fileManager) {
     super(fileManager);
   }