Add ContextPropagatingTaskDecorator

Prior to this commit, `@Async` and `@EventListener` annotated methods
would lose the the logging and observation contexts whenever their
execution was scheduled on a different Thread.

The Context Propagation library supports this use case and can propagate
context values in ThreadLocals, Reactor Context and more.

This commit introduces a new `TaskDecorator` implementation that
leverages the Context Propagation library. When configured on a
`TaskExecutor`, this allows to properly propagate context value through
the execution of the task.

This implementation is completely optional and requires the
"io.micrometer:context-propagation" library on the classpath. Enabling
this feature must be done consciously and sometimes selectively, as
context propagation introduces some overhead.

Closes gh-31130

spring-core/src/main/java/org/springframework/core/task/support/ContextPropagatingTaskDecorator.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2002-2023 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.core.task.support;
+
+import io.micrometer.context.ContextSnapshot;
+import io.micrometer.context.ContextSnapshotFactory;
+
+import org.springframework.core.task.TaskDecorator;
+
+/**
+ * {@link TaskDecorator} that {@link ContextSnapshot#wrap(Runnable) wrap the execution} of
+ * tasks, assisting with context propagation.
+ * <p>This operation is only useful when the task execution is scheduled on a different
+ * thread than the original call stack; this depends on the choice of
+ * {@link org.springframework.core.task.TaskExecutor}. This is particularly useful for
+ * restoring a logging context or an observation context for the task execution. Note that
+ * this decorator will cause some overhead for task execution and is not recommended for
+ * applications that run lots of very small tasks.
+ *
+ * @author Brian Clozel
+ * @since 6.1
+ * @see CompositeTaskDecorator
+ */
+public class ContextPropagatingTaskDecorator implements TaskDecorator {
+
+	private final ContextSnapshotFactory factory;
+
+	/**
+	 * Create a new decorator that uses a default instance of the {@link ContextSnapshotFactory}.
+	 */
+	public ContextPropagatingTaskDecorator() {
+		this(ContextSnapshotFactory.builder().build());
+	}
+
+	/**
+	 * Create a new decorator using the given {@link ContextSnapshotFactory}.
+	 * @param factory the context snapshot factory to use.
+	 */
+	public ContextPropagatingTaskDecorator(ContextSnapshotFactory factory) {
+		this.factory = factory;
+	}
+
+	@Override
+	public Runnable decorate(Runnable runnable) {
+		return this.factory.captureAll().wrap(runnable);
+	}
+
+}