Fix ThreadSPropagationChInterceptor for stacking (#8735)

* Fix ThreadSPropagationChInterceptor for stacking

Related SO thread: https://stackoverflow.com/questions/77058188/multiple-threadstatepropagationchannelinterceptors-not-possible

The current `ThreadStatePropagationChannelInterceptor` logic is to wrap one
message to another (`MessageWithThreadState`), essentially stacking contexts.
The `postReceive()` logic is to unwrap a `MessageWithThreadState`,
therefore we deal with the latest pushed context which leads to the `ClassCastException`

* Rework `ThreadStatePropagationChannelInterceptor` logic to reuse existing `MessageWithThreadState`
and add the current context to its `stateQueue`.
Therefore, the `postReceive()` will `poll()` the oldest context which is, essentially,
the one populated by this interceptor before, according to the interceptors order
* Fix `AbstractMessageChannel.setInterceptors()` to not modify provided list of interceptors
* The new `ThreadStatePropagationChannelInterceptorTests` demonstrates the problem
described in that mentioned SO question and verifies that context are propagated
in the order they have been populated

**Cherry-pick to `6.1.x` & `6.0.x`**

* * Fix `ThreadStatePropagationChannelInterceptor` for publish-subscribe scenario.
Essentially, copy the state queue to a new decorated message
* Fix `BroadcastingDispatcher` to always decorate message, even if not `applySequence`

* * Fix unused import in the `BroadcastingDispatcher`

* * Fix unused import in the `ThreadStatePropagationChannelInterceptor`

spring-integration-core/src/test/java/org/springframework/integration/channel/interceptor/ThreadStatePropagationChannelInterceptorTests.java

@@ -0,0 +1,95 @@
+/*
+ * 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.channel.interceptor;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.task.SyncTaskExecutor;
+import org.springframework.integration.channel.ExecutorChannel;
+import org.springframework.integration.util.ErrorHandlingTaskExecutor;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageChannel;
+import org.springframework.messaging.support.GenericMessage;
+import org.springframework.util.ReflectionUtils;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+/**
+ * @author Artem Bilan
+ *
+ * @since 6.2
+ */
+public class ThreadStatePropagationChannelInterceptorTests {
+
+	@Test
+	void ThreadStatePropagationChannelInterceptorsCanBeStacked() {
+		TestContext1 ctx1 = new TestContext1();
+		TestContext2 ctx2 = new TestContext2();
+
+		List<Object> propagatedContexts = new ArrayList<>();
+
+		var interceptor1 = new ThreadStatePropagationChannelInterceptor<TestContext1>() {
+			@Override
+			protected TestContext1 obtainPropagatingContext(Message<?> message, MessageChannel channel) {
+				return ctx1;
+			}
+
+			@Override
+			protected void populatePropagatedContext(TestContext1 state, Message<?> message, MessageChannel channel) {
+				propagatedContexts.add(state);
+			}
+
+		};
+
+		var interceptor2 = new ThreadStatePropagationChannelInterceptor<TestContext2>() {
+			@Override
+			protected TestContext2 obtainPropagatingContext(Message<?> message, MessageChannel channel) {
+				return ctx2;
+			}
+
+			@Override
+			protected void populatePropagatedContext(TestContext2 state, Message<?> message, MessageChannel channel) {
+				propagatedContexts.add(state);
+			}
+
+		};
+
+		ExecutorChannel testChannel = new ExecutorChannel(
+				new ErrorHandlingTaskExecutor(new SyncTaskExecutor(), ReflectionUtils::rethrowRuntimeException));
+		testChannel.setInterceptors(List.of(interceptor1, interceptor2));
+		testChannel.setBeanFactory(mock());
+		testChannel.afterPropertiesSet();
+		testChannel.subscribe(m -> {
+		});
+
+		testChannel.send(new GenericMessage<>("test data"));
+
+		assertThat(propagatedContexts.get(0)).isEqualTo(ctx1);
+		assertThat(propagatedContexts.get(1)).isEqualTo(ctx2);
+	}
+
+	private record TestContext1() {
+	}
+
+	private record TestContext2() {
+	}
+
+}