fix virtual screens in wayland

xdg-desktop-portal-kde as of this writing is hardcoded to only create 1920x1080 virtual screens in wayland.

specific line:

stream = WaylandIntegration::startStreamingVirtual(output.uniqueId(), {1920, 1080}, cursorMode);

this might have been fine in the past but we are now using virtual screens more and more, in my case using META QUEST 3 oculus with immersed in a virtual desktop streaming scenario.

in gnome, the virtual screens are properly implemented:

could you fix this implementation and allow for multiple resolution when triggering virtual screen in wayland plasma?

i also opened a bug report here: 485850 – xdg-desktop-portal-kde virtual screens hardcoded to 1920x1080