Support scaling in BackgroundContrast effect
Summary:
Background contrast reads pixels from the framebuffer
we need to convert from compositor to framebuffer co-ordinates
when an output is scaled
Test Plan:
Ran the manual test in kwindowsystem. Moved window over dolphin.
Visually checked output
Reviewers: Plasma
Subscribers: plasma-devel, kwin, KWin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D4949