Move `async fn` arguments into closure.

This commit takes advantage of `AsyncArgument` type that was added in a
previous commit to replace the arguments of the `async fn` in the HIR
and add statements to move the bindings from the new arguments to the
pattern from the old argument.

For example, the async function `foo` below:

    async fn foo((x, _y): (T, V)) {
        async move {
        }
    }

becomes:

    async fn foo(__arg0: (T, V)) {
        async move {
            let (x, _y) = __arg0;
        }
    }

0 files changed, 0 insertions, 0 deletions