Draft: [applets/batterymonitor] Fix it, pt.17: Add workaround for freely scrollable sliders

This should prevent keyboard brightness and power profile sliders from getting fractional values during onMoved due to QTBUG-93081.

However, this makes it virtually impossible to actually change slider's value using scrolling now, except for jumping straight to min or max value in one event. But we can always add a MouseArea or WheelHandler on top of PC3.Slider as the ultimate workaround.

CC @ndavis