Add a way to shutdown SyncIoBridge

[imlk0]

Is your feature request related to a problem? Please describe.
SyncIoBridge(#4146) does not provide a way to call the shutdown() function of its internal tokio::io::AsyncWrite instance.

Describe the solution you'd like
Add a shutdown() function to SyncIoBridge, which invoke the shutdown() function of src field

Describe alternatives you've considered
n/a

Additional context
Take tokio::io::DuplexStream as en example. Its shutdown() can be used to close the writer of stream, but in the following example, I have no way to shutdown:

let (s1, _s2) = tokio::io::duplex(1024);
let (rh, wh) = tokio::io::split(s1);
tokio::task::spawn_blocking(move || {
    let mut wh = SyncIoBridge::new(wh);
    // wh.write_all() ...
    // Now I need to shutdown the write half
    wh.shutdown(); // I need this function
});

[imlk0]

@Darksonn What do you think about the proposal to add SyncIoBridge::shutdown()? If appropriate, I can create a PR for this.

[Darksonn]

Adding a method for this sounds good to me.