kstyle: fix qqc2 desktop style sliders in RtL
We don't do any mirroring of the slider groove rects or tickmarks based on layout direction, and this causes qqc2-desktop-style sliders to render in the wrong direction. Swapping the leftRect and the rightRect when option->direction == Qt::RightToLeft fixes this.
This wasn't broken with QWidgets because QSlider relies on (ab)using the upsideDown option in order to achieve mirroring of the groove instead of option->direction, and consequently, this change doesn't affect Qt widgets apps at all.
Edited by Jan Blackquill