Disable window rule configuration for Wayland

Summary:
The window rule detection is too bound to X11 for it to work for
Wayland windows. In fact it results in the config module just crashing.
Thus it's better to just disable the items in the menu. As it's only for
X11 windows we can also enforce platform xcb for the rules dialog.

Test Plan: Menu disabled on Wayland window, menu enabled on Xwayland window

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10594