Remove gtest file from cpp library (apache#9816)

* Fix the apache-rat check
---

**Motivation**

PR apache#9072 introduces the gtest file but does not exclude for apache-rat
check. So that causes the apache-rat check to fail.

* Move the test to the another file

* Address comments

pom.xml

@@ -1241,7 +1241,6 @@ flexible messaging model and an intuitive client API.</description>
                 <exclude>logs/**</exclude>
                 <exclude>**/circe/**</exclude>
                 <exclude>pulsar-broker/src/test/resources/authentication/basic/.htpasswd</exclude>
-                <exclude>pulsar-client-cpp/include/gtest/gtest_prod.h</exclude>
                 <exclude>pulsar-client-cpp/lib/checksum/int_types.h</exclude>
                 <exclude>pulsar-client-cpp/lib/checksum/gf2.hpp</exclude>
                 <exclude>pulsar-client-cpp/lib/checksum/crc32c_sse42.cc</exclude>

pulsar-client-cpp/lib/MultiTopicsConsumerImpl.h

@@ -18,7 +18,7 @@
  */
 #ifndef PULSAR_MULTI_TOPICS_CONSUMER_HEADER
 #define PULSAR_MULTI_TOPICS_CONSUMER_HEADER
-#include "gtest/gtest_prod.h"
+#include "lib/TestUtil.h"
 #include "ConsumerImpl.h"
 #include "ClientImpl.h"
 #include "BlockingQueue.h"

pulsar-client-cpp/lib/PartitionedConsumerImpl.h

@@ -18,7 +18,7 @@
  */
 #ifndef PULSAR_PARTITIONED_CONSUMER_HEADER
 #define PULSAR_PARTITIONED_CONSUMER_HEADER
-#include "gtest/gtest_prod.h"
+#include "lib/TestUtil.h"
 #include "ConsumerImpl.h"
 #include "ClientImpl.h"
 #include <vector>

pulsar-client-cpp/lib/TestUtil.h

@@ -0,0 +1,25 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+#ifndef PULSAR_CPP_TESTUTIL_H
+#define PULSAR_CPP_TESTUTIL_H
+
+#define FRIEND_TEST(test_case_name, test_name) friend class test_case_name##_##test_name##_Test
+
+#endif  // PULSAR_CPP_TESTUTIL_H

pulsar-client-cpp/lib/UnAckedMessageTrackerEnabled.h

@@ -18,7 +18,7 @@
  */
 #ifndef LIB_UNACKEDMESSAGETRACKERENABLED_H_
 #define LIB_UNACKEDMESSAGETRACKERENABLED_H_
-#include "gtest/gtest_prod.h"
+#include "lib/TestUtil.h"
 #include "lib/UnAckedMessageTrackerInterface.h"
 
 #include <mutex>