Function save_bytes 

pub fn save_bytes(
    title: &'static str,
    suggested_name: String,
    extensions: &'static [&'static str],
    data: Vec<u8>,
    on_done: Box<dyn FnOnce(SaveOutcome) + Send + 'static>,
)

Non-blocking save dialog that writes data. Works on every target. on_done is called with the outcome after the OS finishes.