Large Scroll Moves are incorrectly reported in DemoScroll

[mkromberg]

Clicking beside the thumb in a Scroll is supposed to generate a "large move", at the moment it generates a move to the position where the mouse click happened.

Start DemoScroll and click twice in the same position about halfway down the vertical scroll bar. Notice the two scroll messages which both set the position to 568.

{"Event":{"EventName":"Scroll","ID":"F1.UPDOWN","EventID":"53d2058c-83a5-4dc9-84f5-07ef2861117e","Info":[2,568]}}
{"Event":{"EventName":"Scroll","ID":"F1.UPDOWN","EventID":"c151420e-61e1-4fad-9007-3fff2376c335","Info":[-2,568]}}

The correct behaviour for a click outside the thumb is to move the thumb as far as the second element of the Step property defines, while clicking on an arrowhead should move according to the first element. We do not support this property, but agreed that it should default to [1,10] a long time ago, and this was working until recently.

In other words, if the Thumb is at 1 and you click below the thumb, the events should report [2,11] for the first click, [2,21] for the next, etc - moving by 10 each time.

More information at https://help.dyalog.com/latest/Content/GUI/Properties/Step.htm.