Support fractional scailng in KScreen Scaling preview
Summary:
Qt 5.something changed to support fractional scaling.
I updated the backend code to support that, I never updated the preview
UI.
Test Plan: Moved the slider, and it looked awesome
Reviewers: Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D5412