feat(generator): switch resumable upload specialized stubs to package private

Author: whowes

java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/stub/HttpJsonResumableUploadServiceResumableUploadStub.java

@@ -54,7 +54,7 @@
 @InternalApi
 @NullMarked
 @BetaApi
-public class HttpJsonResumableUploadServiceResumableUploadStub implements BackgroundResource {
+class HttpJsonResumableUploadServiceResumableUploadStub implements BackgroundResource {
   private static final TypeRegistry typeRegistry = TypeRegistry.newBuilder().build();
 
   private static final ApiMethodDescriptor<UploadMediaRequest, UploadMediaResponse>

sdk-platform-java/gapic-generator-java/src/main/java/com/google/api/generator/gapic/composer/rest/HttpJsonServiceResumableUploadStubClassComposer.java

@@ -270,7 +270,7 @@ public GapicClass generate(GapicContext context, Service service) {
             .setPackageString(pakkage)
             .setHeaderCommentStatements(createClassHeaderComments(service))
             .setAnnotations(createClassAnnotations(service))
-            .setScope(ScopeNode.PUBLIC)
+            .setScope(ScopeNode.LOCAL)
             .setName(className)
             .setImplementsTypes(
                 Arrays.asList(FIXED_TYPESTORE.get(BackgroundResource.class.getSimpleName())))

sdk-platform-java/gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/rest/goldens/HttpJsonMediaServiceResumableUploadStub.golden

@@ -38,7 +38,7 @@ import org.jspecify.annotations.NullMarked;
 @InternalApi
 @NullMarked
 @BetaApi
-public class HttpJsonMediaServiceResumableUploadStub implements BackgroundResource {
+class HttpJsonMediaServiceResumableUploadStub implements BackgroundResource {
   private static final TypeRegistry typeRegistry = TypeRegistry.newBuilder().build();
 
   private static final ApiMethodDescriptor<UploadMediaRequest, UploadMediaResponse>