chore: add a regression test for WASI (#4822)

Currently, we only have WASM regression tests that run without WASI.
However, rust provides a WASI specific target which enables code to
special case WASI. This PR adds a basic test to cover that case.

This is an initial addition to help land tokio-rs/tokio#4716.

tests-integration/tests/macros_main.rs

@@ -1,4 +1,4 @@
-#![cfg(all(feature = "macros", feature = "rt"))]
+#![cfg(all(feature = "macros", feature = "rt-multi-thread"))]
 
 #[tokio::main]
 async fn basic_main() -> usize {

tests-integration/tests/rt_yield.rs

@@ -0,0 +1,41 @@
+use tokio::sync::oneshot;
+use tokio::task;
+
+async fn spawn_send() {
+    let (tx, rx) = oneshot::channel();
+
+    let task = tokio::spawn(async {
+        for _ in 0..10 {
+            task::yield_now().await;
+        }
+
+        tx.send("done").unwrap();
+    });
+
+    assert_eq!("done", rx.await.unwrap());
+    task.await.unwrap();
+}
+
+#[tokio::main(flavor = "current_thread")]
+async fn entry_point() {
+    spawn_send().await;
+}
+
+#[tokio::test]
+async fn test_macro() {
+    spawn_send().await;
+}
+
+#[test]
+fn main_macro() {
+    entry_point();
+}
+
+#[test]
+fn manual_rt() {
+    let rt = tokio::runtime::Builder::new_current_thread()
+        .build()
+        .unwrap();
+
+    rt.block_on(async { spawn_send().await });
+}