effects/morphingpopups: Fix glitch

There's a visual glitch that looks like a random rectangle in the top left corner of morphing popup. It appears like it's caused by the blur effect, it produces wrong results when the window is captured in CrossFadeEffect::redirect().

Make CrossFadeEffect::redirect() unset blur and contrast force roles, so the backdrop effects are not included in the captured frame.

Draft: I don't like it