Extract into function assist fails to add .await when extracting an async fn

[jplatte]

Since #8766, extracting some code into a function generates an async fn if that code includes a .await point. However, the call to the generated function is not .awaited, leading to the code not compiling in many cases, or even the code still compiling but the async task not being executed. For example, when extracting

tokio::time::sleep(Duration::from_millis(50)).await;

as sleep50ms, the call ends up as just

sleep50ms();

when it should be

sleep50ms().await;

[jplatte]

cc @JamieCunliffe who implemented #8766.