Support vertical sliders on Android

There is no such thing as a vertical slider in the native Android
style. Therefore, we need to rotate the painter in order to draw
one.

Task-number: QTBUG-41992
Change-Id: Ibe2bf1d7fa27756aad0b8469c8752d6d3e848527
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>