Greatly improve scroll experience on trackpads

[Tyriar]

Adds support for diagonal and ballistic (smooth) scroll events:

Fixes #228
Fixes #227

[Tyriar]

I didn't test this with a mouse, it will probably end up scrolling multiple lines on some machines/browsers, depending on how they fire WheelEvent.

[lramos15]

Thanks! The gif looks really smooth :)

[lramos15]

I can test it on a mouse, give me a few minutes

[lramos15]

Yeah I would say with a mouse wheel it feels a lot more broken than it does on main. You can scroll super slowly but anything else you jump multiple lines. I would recommend you try it if possible to see what I mean

[lramos15]

Want to hold off on merging this until we get a better experience for both mouse and trackpad. As this seems to trade one for the other.

[Tyriar]

Sounds good, I'll improve on mouse a bit later.

[Tyriar]

@lramos15 ready for another one, not the best fix as it's much harder than you'd expect to differentiate hardware wheel/trackpad, but it should make the experience good on mac.

[lramos15]

Seems like a better fix to me and I'm happy to have trackpad support. Will need to look into something similar to xterm.js in the future to increase the experience even more by always snapping to a line.

[Tyriar]

Ref for future: https://github.com/xtermjs/xterm.js/blob/145b4874cb217d7c23b46c731a2bb9a780b66c3f/src/browser/Viewport.ts#L27-L30