Optimize SpEL and property placeholder support for @Async qualifiers

See gh-27818
Closes gh-28549

spring-context/src/test/java/org/springframework/scheduling/annotation/EnableAsyncTests.java

@@ -146,6 +146,9 @@ public class EnableAsyncTests {
 
 			Future<Thread> workerThread2 = asyncBean.myWork2();
 			assertThat(workerThread2.get().getName()).startsWith("myExecutor2-");
+
+			Future<Thread> workerThread3 = asyncBean.defaultExecutor();
+			assertThat(workerThread3.get().getName()).startsWith("SimpleAsyncTaskExecutor");
 		}
 		finally {
 			System.clearProperty("myExecutor");
@@ -382,6 +385,11 @@ public class EnableAsyncTests {
 		public Future<Thread> myWork2() {
 			return new AsyncResult<>(Thread.currentThread());
 		}
+
+		@Async("${my.app.targetExecutor:}")
+		public Future<Thread> defaultExecutor() {
+			return new AsyncResult<>(Thread.currentThread());
+		}
 	}