This patch ports the KCM almost entirely to QQC2. The QQC1 stragglers are `ScrollView`, `TabView`, and `Tab`, which don't seem to be available in QQC2 (?)
This has the side effect of working around https://bugreports.qt.io/browse/QTBUG-70481 and improving the presentation for people using fractional Qt scale factors.
BUG: 397954
FIXED-IN: 5.15.0