GH-3869: Add ContextHolderRequestHandlerAdvice

Fixes https://github.com/spring-projects/spring-integration/issues/3869

* Move `ContextHolderRequestHandlerAdvice` to the `core` module for more general purposes
* Add `ContextHolderRequestHandlerAdviceTests`
* Rework `DelegatingSessionFactoryTests` to rely on the `ContextHolderRequestHandlerAdvice`.
This allows us to remove unnecessary XML configuration for this test class
* Document the feature

spring-integration-core/src/test/java/org/springframework/integration/handler/advice/ContextHolderRequestHandlerAdviceTests.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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.
+ */
+
+package org.springframework.integration.handler.advice;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.aop.framework.ProxyFactoryBean;
+import org.springframework.messaging.MessageHandler;
+import org.springframework.messaging.support.GenericMessage;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Artem Bilan
+ *
+ * @since 6.1
+ */
+public class ContextHolderRequestHandlerAdviceTests {
+
+	@Test
+	void contextHolderRequestHandlerAdviceInAction() {
+		AtomicReference<Object> context = new AtomicReference<>();
+
+		AtomicReference<Object> valueFromHandler = new AtomicReference<>();
+		MessageHandler testHandler = message -> valueFromHandler.set(context.get());
+
+		String testContextValue = "test data";
+
+		ContextHolderRequestHandlerAdvice contextHolderRequestHandlerAdvice =
+				new ContextHolderRequestHandlerAdvice(m -> testContextValue, context::set, () -> context.set(null));
+
+		ProxyFactoryBean fb = new ProxyFactoryBean();
+		fb.setTarget(testHandler);
+		fb.addAdvice(contextHolderRequestHandlerAdvice);
+		testHandler = (MessageHandler) fb.getObject();
+
+		testHandler.handleMessage(new GenericMessage<>(""));
+
+		assertThat(valueFromHandler.get()).isEqualTo(testContextValue);
+		assertThat(context.get()).isNull();
+	}
+
+}