[effects/thumbnailaside] Use windowFrameGeometryChanged
Summary:
Use windowFrameGeometryChanged rather than windowGeometryShapeChanged
because we are interested only in frame geometry changes.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D26906