Configuration options for virtual threads (on JDK 21)

VirtualThreadDelegate built on JDK 21 for multi-release jar.
Includes dedicated VirtualThreadTaskExecutor as lean option.
Includes setVirtualThreads flag on SimpleAsyncTaskExecutor.
Includes additional default methods on AsyncTaskExecutor.

Closes gh-30241

spring-context/src/main/java/org/springframework/scheduling/concurrent/ThreadPoolTaskExecutor.java

@@ -364,12 +364,6 @@ public class ThreadPoolTaskExecutor extends ExecutorConfigurationSupport
 		}
 	}
 
-	@Deprecated
-	@Override
-	public void execute(Runnable task, long startTimeout) {
-		execute(task);
-	}
-
 	@Override
 	public Future<?> submit(Runnable task) {
 		ExecutorService executor = getThreadPoolExecutor();

spring-context/src/main/java/org/springframework/scheduling/concurrent/ThreadPoolTaskScheduler.java

@@ -282,12 +282,6 @@ public class ThreadPoolTaskScheduler extends ExecutorConfigurationSupport
 		}
 	}
 
-	@Deprecated
-	@Override
-	public void execute(Runnable task, long startTimeout) {
-		execute(task);
-	}
-
 	@Override
 	public Future<?> submit(Runnable task) {
 		ExecutorService executor = getScheduledExecutor();