Widgets: Sliders & Drags display the value in a tooltip on touchscreens.

Hello Omar,

Long time no talk ;-)

On a touchscreen, the finger often hides the value inside a slider or a drag. We now display the value in a tooltip, if and only if using a touchscreen, and while the finger holds the widget.

Thanks to fixes following #8036, the tooltip is correctly displayed above the finger.

See screenshot below:

Cheers!