input: Fix scroll speed for internal wheel events
Qt expects angleDelta 120 be one "click" whereas libinput uses 15, hence multiply by 8.
This is also what Qt does in eglfs libinput backend.
No idea how the “v120” stuff is supposed to work but for me it was always zero.
With this, scrolling through the kwin debug console feels identical to scrolling a regular Qt app, tested both with laptop touchpad and a mouse with discrete wheel clicks.
Edited by Kai Uwe Broulik