A way to set app_id on Wayland is needed

[nicolasfella]

On Wayland the set_app_id request in xdg shell allows to set the desktop file name for an app: https://wayland.app/protocols/xdg-shell#xdg_toplevel:request:set_app_id

Setting the right value here is important for desktop apps, for a number of reasons. See https://nicolasfella.de/posts/importance-of-desktop-file-mapping/ for details on that.

Slint should expose a way to set this app id, similar to QGuiApplication::setDesktopFileName()