autotests: Rework _KDE_NET_WM_SCREEN_EDGE_SHOW tests
I'd like to rework Window::showOnScreenEdge()
, specifically get rid of it to decouple screen edge logic from Window. But, there are no tests that check the interaction between WM stuff and the client side, e.g. removing _KDE_NET_WM_SCREEN_EDGE_SHOW property.