[libkwineffects] Port AnimationEffect to TimeLine
Summary:
TimeLine has nice API for controlling its direction that can be re-used
later by AnimationEffect.
Test Plan: The existing tests for scripting effects still pass.
Reviewers: KWin, davidedmundson, graesslin
Reviewed By: KWin, davidedmundson, graesslin
Subscribers: davidedmundson, abetts, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D16448