[effects/squash] Try to reverse previous active animations

Summary:
If a window is unminimized and the minimize animation is still active,
don't cancel the latter and start a new animation. Instead, try to
reverse already active animation and if that attempt failed, start a new
animation. This results in more smoother animations.

Reviewers: KWin, davidedmundson

Reviewed By: KWin, davidedmundson

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D16451