Reduce use of KWindowSystem on Wayland

BUG:402634
BUG:381541

This patchset was originally part of MR !81.

Problem description: Currently most of KWindowSystem standard API does not work on Wayland, on purpose - the code for Wayland support was actually removed from the KWindowSystem framework into a standalone [plasma/kwayland-integration](https://invent.kde.org/plasma/kwayland-integration) where [src/windowsystem/windowsystem.cpp](https://invent.kde.org/plasma/kwayland-integration/-/blob/master/src/windowsystem/windowsystem.cpp) has almost all API implementations empty and just issue warnings in the form of "This plugin does not support...".

Additionally, in [bug report 442662: KWindowSystem on Wayland is missing many signals, some of which are needed by Yakuake](https://bugs.kde.org/show_bug.cgi?id=442662#c1) David Edmundson says "Wayland is different, trying to shoehorn that into the exact same abstractions simply won't work. Lets split this up as individual bugs on yakuake".

So this is some of that work of changing Yakuake Wayland behavior to not rely on non-working (or mostly non-working) KWindowSystem and replace with operations using Wayland APIs directly, or Qt API that is known to work with Wayland.

This patch set is not complete in that:
a. There are some operations that are as of yet not possible under Wayland (for example - set visible on all desktops), so removing those code calls under Wayland will hide warnings that we may want to keep to remind us there is missing behavior.
b. There are still some wayland-integration warnings that are shown when running Yakuake on kwin_wayland. I did not work on these because changes do not affect my use case (also see (a) above). If there is need, I can review more APIs and do more KWindowSystem reduction.