Revert "fix: privately-scoped vars in ServiceClientTest codegen (#377)"

This reverts commit c004e9c.

Author: miraleung

src/main/java/com/google/api/generator/gapic/composer/ServiceClientTestClassComposer.java

@@ -186,7 +186,7 @@ private static List<Statement> createClassMemberFieldDecls(
                 ExprStatement.withExpr(
                     v.toBuilder()
                         .setIsDecl(true)
-                        .setScope(ScopeNode.PRIVATE)
+                        .setScope(ScopeNode.PUBLIC)
                         .setIsStatic(v.type().reference().name().startsWith("Mock"))
                         .build()))
         .collect(Collectors.toList());

src/test/java/com/google/api/generator/gapic/composer/goldens/EchoClientTest.golden

@@ -37,10 +37,10 @@ import org.junit.Test;
 
 @Generated("by gapic-generator-java")
 public class EchoClientTest {
-  private static MockServiceHelper mockServiceHelper;
-  private static MockEcho mockEcho;
-  private EchoClient client;
-  private LocalChannelProvider channelProvider;
+  public static MockServiceHelper mockServiceHelper;
+  public static MockEcho mockEcho;
+  public EchoClient client;
+  public LocalChannelProvider channelProvider;
 
   @BeforeClass
   public static void startStaticServer() {