This is second part of D15175: [effects/cubeslide] Fix visual glitches with Blur / BackgroundContrast effect, and aimed at fixing Bug 390366.
The problem was that effect relied on isManaged() to detect OSDs and notifications, that should be painted on top of the cube. On Wayland, the desktop window itself is not managed, which made it "sticky".
Instead we use isSpecialWindow() check to explicitly make notifications and OSDs sticky.
BUG: 390366
FIXED-IN: 5.15.0