Polish "Alias auto-configured `TaskExecutor` to make async tasks use it"

Closes gh-15748

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/task/TaskExecutionAutoConfiguration.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -30,6 +30,7 @@ import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.core.task.TaskDecorator;
 import org.springframework.core.task.TaskExecutor;
+import org.springframework.scheduling.annotation.AsyncAnnotationBeanPostProcessor;
 import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
 
 /**
@@ -49,8 +50,6 @@ public class TaskExecutionAutoConfiguration {
 	 */
 	public static final String APPLICATION_TASK_EXECUTOR_BEAN_NAME = "applicationTaskExecutor";
 
-	public static final String ASYNC_TASK_EXECUTOR_BEAN_NAME = "taskExecutor";
-
 	private final TaskExecutionProperties properties;
 
 	private final ObjectProvider<TaskExecutorCustomizer> taskExecutorCustomizers;
@@ -82,7 +81,8 @@ public class TaskExecutionAutoConfiguration {
 	}
 
 	@Lazy
-	@Bean(name = { APPLICATION_TASK_EXECUTOR_BEAN_NAME, ASYNC_TASK_EXECUTOR_BEAN_NAME })
+	@Bean(name = { APPLICATION_TASK_EXECUTOR_BEAN_NAME,
+			AsyncAnnotationBeanPostProcessor.DEFAULT_TASK_EXECUTOR_BEAN_NAME })
 	@ConditionalOnMissingBean(Executor.class)
 	public ThreadPoolTaskExecutor applicationTaskExecutor(TaskExecutorBuilder builder) {
 		return builder.build();

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/task/TaskExecutionAutoConfigurationTests.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.