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