No option to set different deceleration values for mouse wheel and touchpad scrolling

This commit added the option to set the env variable QT_QUICK_FLICKABLE_WHEEL_DECELERATION to control  flickable deceleration speed, but the outcome is that it set it for BOTH mouse wheel and touchpad events.

Therefore, when I set that env variable to a high number (e.g. 3000) to make the touchpad scrolling go smoother, my users (get-notes.com) complain that the mouse wheel should NOT decelerate the same way. But when I disable it, they complain that touchpad scrolling is too slow and "stiff".

The solution will be to have two different env variables, one for mouse-wheel scrolling and another for touchpad.

I've tried setting the flickDeceleration property, thinking this should be the one controlling the touchpad scrolling speed on my ListView, but it has no effect whatsoever, at least on Desktop.

For some reason, on macOS, the default settings, without setting the env variable or other settings, seems to work okay both for mouse wheel and touchpads. But it will still be nice to be able to set it separately there as well.