glib: Add #[weak_no_upgrade] that requires manual upgrades in the body

[sdroege]

Use case is something like this

    glib::spawn_future_local(clone!(
        #[weak]
        button,
        async move {
            while let Ok(enable_button) = receiver.recv().await {
                button.set_sensitive(enable_button);
            }
        }
    ));

The intention here clearly is that this is stopped to be called when the button goes away, but that is not the case. The future will always have a strong reference to the button once it was called for the first time and the button can never go away.

Something like this would be needed

    glib::spawn_future_local(clone!(
        #[weak_no_upgrade]
        button,
        async move {
            while let Ok(enable_button) = receiver.recv().await {
                let Some(button) = button.upgrade() else {
                    break;
                };
                button.set_sensitive(enable_button);
            }
        }
    ));