Add run_until_cancelled_owned to CancellationToken

[tysen]

Pretty natural addition to match the cancelled_owned fn.

Motivation

let token = CancellationToken::new();
tokio::spawn(token.run_until_cancelled(my_async_fn())); // doesn't compile
tokio::spawn(async move { // current workaround
    token.run_until_cancelled(my_async_fn())).await
});
tokio::spawn(token.run_until_cancelled_owned(my_async_fn())); // compiles, looks nicer

Solution

Just a carbon copy of the existing fn switching to the appropriate cancellation future.