Fix global menu for Xwayland windows

Someone in IRC reported that some X11 applications don't have a global menu in a Plasma Wayland session, but they appear in an X11 session just fine. (Is there a report on bugs.kde.org for that?)

I was able to reproduce that and found that kded5 -platform xcb --replace helped and came up with this code.

I'm wondering why the xprops are even used by anything, is the GetMenuForWindow method not enough?

PoC because the KWindowInfo part won't work, so window type and class are unknown.