Improve the feel of the smooth scrolling feature

From @YuriSizov on #1048

> In my own testing (though I'm on Windows), speed-wise scrolling is fine with a mouse wheel. Both in Chrome and in Firefox (fullscreen in both). It is pretty awful in terms of smoothness though, very jittery. Either browser covers similar distance with similar inputs, but either browser also does it in very noticeable steps, per scroll update. It's like turning a ratchet, if you know the feeling. This happens even with unlocked FPS (I haven't double-checked what unlocking does right now though).
>
> So that is something we should still look into improving, I think.

The feel of the scrolling seems to depend still on the device and the speed setting on this end with relatively low to medium scrolling speed settings and with a mouse wheel the smooth scrolling is working fairly well as intended. If I try to scroll really fast this is when it gets the most jittery with a mouse. And with a touchpad, it's a bit more sensitive. I feel it tends to happen maybe a little more. In any case, there is definitely room for improvement.

~Related task (for when someone picks this up): #944

No implementation file or test is named. Start by reading related issues #1048 and #944, then reproduce mouse-wheel and touchpad scrolling at different speeds. Done means scrolling feels smooth rather than jittery across the reported browser and device cases.

Written by the indexing model from the issue text.