Move lanczos filter away from KWin core
Summary:
Lanczos filter shouldn't be in KWin core because it's quite specific about
rendering backend.
Test Plan: Windows in the desktop grid look normal.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: mart, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D18774