feat(wayland): popup window

[wusyong]

While we can use muda to create context menu, it requires GTK as dependency.
We want to go with more native approach so I'm researching smithay-client-toolkit at the moment.
According to wayland protocol, we need to get window's wl_surface and obtain xdg_surface for it.
This means we also needs to get the xdg_wm_base global, but smithay_client_toolkit doesn't seem to have anywhere to explain how to get this.
The rests steps are almost from the method of xdg_wm_base as well.

If we could get the wl_surface of the popup window, we can think about how to add it into our Window type. Hence, it will be able to become a webview and render the menu we want to display.

[wusyong]

See also: Smithay/client-toolkit#471

[pewsheen]

Currently I can create an xdg_popup from smithay-client-toolkit
pewsheen/client-toolkit@373e637

But I'm unsure if I'm using it correctly, and it needs delegated seats to handle input as well.

I think the next step will be using it with Winit. But it seems that Winit has not re-exposed those Wayland states; we will figure it out in the following days.

[pewsheen]

Okay! I made a workable version that modified from Winit example
pewsheen/winit@73fad21

Unfortunately, it requires implementing some traits to the WinitState in the Winit crate. Hence, we may not be able to create the popup at the moment, or maybe someone else has ideas 🙏