Implemented smooth scrolling.

[PoetaKodu]

Hello everyone.

I implemented smooth scrolling. I was annoyed that every time I scroll terminal in VS Code I lose track (see #1140 and microsoft/vscode#125950).
The option is disabled by default but can be enabled using terminal options.

Preview:
https://youtu.be/BCYdZwydmLw

[Tyriar]

@PoetaKodu very cool 👍 will try get a review done this week/early next week. The main thing I want to check out is how the settings work, trackpad vs wheel and how close the experience is to monaco.

[Eugeny]

Tested and trackpad scrolling isn't affected by the new option 👍

[Tyriar]

Looking into this now, my first impressions are:

• The scroll speed is too slow, looks like monaco has a smooth scroll duration of 125ms and it feels a lot more responsive because of that
• smoothScrollingStepInterval seems like we don't need it and it should instead be replaced by requestAnimationFrame
• A duration would be preferable to smoothScrollingSpeed, so the pointer device tells the terminal how much to scroll and smooth scroll animates that over x milliseconds. If the animation happens based on a number of lines each frame then scrolling a large amount of lines seems like it would be a bad experience?

[Tyriar]

Yeah the above is my main feedback, it would be better to move to duration-based scrolling and we should use requestAnimationFrame instead of setTimeout/setInterval. Interested in your thoughts, thanks!

[Tyriar]

Implemented the needed changes in #3940