Add some tolerances to breadcrumb scrolling

[turt2live]

See element-hq/element-web#9400
See element-hq/element-web#9394

Tolerances are defined as a device-only setting to give advanced users an option to override the values. No UI is exposed for this.

The default values are picked for assumptions on comfort, however as people change the tolerances themselves the defaults may need to change.

[dbkr]

Hmm - do we know how common a problem this is? If it's something that's going to affect a lot of people, telling them to tweak some values in their config doesn't really seem like a good solution. Also, presumably tis behaviour differs between trackpad / scroll wheel? In which case you'd tweak the values for one and then plug in / unplug a mouse and have to undo the tweaking again?

[turt2live]

It's a common problem for at least 2 people. The two variables are meant to solve the two separate problems: xyThreshold is meant to solve the trackpad problem whereas yReduction is meant to solve the scroll wheel problem. Plugging in a mouse would probably cause the tolerances to be outdated for the user, however I don't think the impact will be severe enough for them to notice. Can we even detect which device the user is using or when it changes?

The tolerances setting is more meant for us to try and work out sensible defaults. For instance, if people complain that the horizontal scroll is too fast after this then we can recommend they play with the settings to come up with numbers they like and we can use that to influence the defaults. To me this is preferable because it means less PRs with titles of "change yReduction to 0.65". The eventual plan is to either give the setting proper UI (if we want that) or remove it (if we don't want the UI).

[dbkr]

Fair enough if it's so we can experiment & get the defaults right. Mostly my surprise is that a horizontal scroller needs special parameters tweaked rather than just being a native browser scrolling element.

[turt2live]

It is a native scrolling element, but the this._scrollElement.scrollLeft += e.deltaY * yReduction; is what I think is throwing off the calculations. Humans aren't perfect (sadly), so there's probably some vertical component to their scroll which is causing excessive scrolling.