xdg_toplevel should be accessible via nativeResourceForWindow

On Wayland, when using xdg_shell integration, xdg_toplevel should be accessible via nativeResourceForWindow call - similar to how wl_shell_surface is accessible in wl_shell integration. This allows for custom drag regions for the application window.

xdg_toplevel = static_cast<struct xdg_toplevel *>(
native->nativeResourceForWindow("xdg_toplevel", window));