Implement a join_all convenience function

[FalkWoldmann]

Is your feature request related to a problem? Please describe.
In issue #6664, the convenience method join_all was introduced for the JoinSet. To enhance this further, it would be nice to implement a join_all function that accepts any type implementing IntoIterator and containing futures. This would improve usability and convenience. This would be similar to the join_all function from the futures crate.

Describe the solution you'd like
I came up with the following:

pub async fn join_all<T: Send + 'static>(futures: impl IntoIterator<Item=impl Future<Output=T> + Send + 'static>) -> Vec<T> {
    futures.into_iter().collect::<JoinSet<T>>().join_all().await
}

The question would be, where to put this function. Perhaps to tokio::task?

[Noah-Kennedy]

tokio-util is probably a better place for this if we were to do it

We try and keep these sorts of utility things outside of the main crate generally.