task: add AbortOnDropHandle type (#6786)

tokio-util/tests/abort_on_drop.rs

@@ -0,0 +1,27 @@
+use tokio::sync::oneshot;
+use tokio_util::task::AbortOnDropHandle;
+
+#[tokio::test]
+async fn aborts_task_on_drop() {
+    let (mut tx, rx) = oneshot::channel::<bool>();
+    let handle = tokio::spawn(async move {
+        let _ = rx.await;
+    });
+    let handle = AbortOnDropHandle::new(handle);
+    drop(handle);
+    tx.closed().await;
+    assert!(tx.is_closed());
+}
+
+#[tokio::test]
+async fn aborts_task_directly() {
+    let (mut tx, rx) = oneshot::channel::<bool>();
+    let handle = tokio::spawn(async move {
+        let _ = rx.await;
+    });
+    let handle = AbortOnDropHandle::new(handle);
+    handle.abort();
+    tx.closed().await;
+    assert!(tx.is_closed());
+    assert!(handle.is_finished());
+}