board settings: allow sliders to be adjusted with mouse wheel

[AAArmstark]

It's difficult to make precise adjustments by clicking in or dragging the board settings sliders (size, brightness, hue)

keyboard arrows are the only way to do this precisely at the moment, the mouse wheel would be a comfortable alternative

[icp1994]

Or have a input box.

[schlawg]

It's not photoshop, think of it more like a "drag till you think the board looks better kinda thing."

[schlawg]

gah, i suppose there's no harm

[schlawg]

An input box is ideal but we don't want to sacrifice room needed for newer boards. Total menu size is constrained by small phones.

However, we could turn the labels (brightness/zoom/hue) into buttons that popup an input box where you could edit the value with keyboard. Ideally this would close both #15200 and #15201