Provide native window access, via "fetch_native_handle" method on window.

[dtzxporter]

This should alleviate some of the concerns in: #2194 (comment) because it will force the callback to be ran in the event loop in iced, and gives us a reference to the window directly instead. While the user could mess up the iced state by making changes here, I think that anyone using this method should know what they are doing and it's an advanced use case.

Links:
#2194

[dtzxporter]

Will rework this once #2191 lands.

[hecrj]

Thanks!

[WhyNotHugo]

How does one get from a iced::widget::shader::wgpu::rwh::WindowHandle to something like a wayland_client::protocol::wl_registry::WlRegistry or even a wayland_client::protocol::wl_shell_surface::WlShellSurface?

What about global protocol objects like wl_output?

[hecrj]

You call as_raw, then pattern match on Wayland, and you keep going from there.

https://docs.rs/iced/latest/iced/widget/shader/wgpu/rwh/enum.RawWindowHandle.html#variant.Wayland

[WhyNotHugo]

I looked at that before asking here, but that variant's associated type is:

pub struct WaylandWindowHandle {
    pub surface: NonNull<c_void>,
}

I'm not sure how to operate on a c_void (which is basically a type-erased pointer). Can't this actually be a reference with a proper type instead?