Rhai is unsound (use after free)

Consider the following example:

fn main() {
    let global_name: std::rc::Rc<std::cell::RefCell<&'static str>> = Default::default();
    let global_name2 = global_name.clone();
    {
        let mut engine = rhai::Engine::new();

        engine.register_fn("hello", move |name: &'static str| {
            *global_name.borrow_mut() = name;
        });

        engine.eval::<()>(r#"hello("some name")"#).unwrap();
    }

    println!("{:?}", &*global_name2.borrow());
}

rhai v1.19.0

No source file, test, or entry point is named. Start by reproducing the provided Rust example against rhai v1.19.0, then trace how Engine::register_fn handles the captured callback and the 'static str argument. Done means the example no longer permits use-after-free, with a regression test covering the reported case.