How far the pointer must travel sideways before the movement counts as a
swipe.
Remarks
Roughly a thumb's width: short enough that a deliberate flick always clears
it, long enough that the wander of a tap never does. Exported so a caller —
or a test — reads the same number the hook measures against rather than
keeping a copy that drifts.
How far the pointer must travel sideways before the movement counts as a swipe.