draft: kstyle: unmirror Qt's horizontal scrollbar behaviour in RtL

This seems to be what was originally intended, and may have broken somewhere in the 7 years we've had the QStyle around.

Mirrored horizontal scrollbars don't really make sense, since scrollbars don't relate to text direction, they relate to the positioning of the viewport on a view. If the viewport is on the left of a view, the scrollbar should be on the left, regardless of the text direction.

This is also more consistent with other software handling RtL well, which users will be accustomed to.