[effects/fallapart] Fix flickering problem

Summary:
The Fall Apart effect doesn't grab windows so a conflict could happen
if an alternative window open/close animation effect is enabled(e.g.
Fade, Glide).

Before

Fall apart and Fade conflict with each other.

After

Only Fall apart animates the disappearing of System Settings.

Test Plan:

• Enabled fall apart effect and fade effect
• Closed a window

Reviewers: KWin, davidedmundson

Reviewed By: KWin, davidedmundson

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D13527