We always want the slider to increase its value when scrolling
up or right, no matter the inverted scrolling setting.

For "regular" scrolling, this corresponds to positive values on
the Y axis and negative values on the X axis. For "natural"
scrolling (indicated by the `inverted` property) is the opposite
so we need to reverse the sign.

Note that the Qt documentation on WheelEvent is dubious:
On https://doc.qt.io/qt-5/qml-qtquick-wheelevent.html, the
`angleDelta` section suggests that positive should be up/right,
but the `inverted` section indicates the above mentioned behavior.

BUG: 459624
FIXED-IN: 5.91.0