kwin_wayland and setWindowIcon()

[Eike Hein]

Note that even if this is added, the Task Manager is just going to
ignore it. The Task Manager is written to try and identify the app
that owns a window and use the icon from the .desktop file, to
enable consistent theming (not all apps load icon assets the same
way and set it well on the window on X11) and make sure the icon
stays the same across the launcher <-> startup notification <->
window lifecycle transitions. The window icon is a last resort
fallback path.

kwin_wayland acting like this makes kwin and the TM more consistent,
which is a nice improvement IMHO.


Cheers,
Eike