Support adjustable side scroll amount

[MostlyArmless]

The default amount of sidescroll is 14 columns per mousewheel increment, which is too much and I end up needing to use the mouse to fine-tune the horizontal position anyways.

Suggest you either make the side scroll amount configurable or default it to a smaller increment.

[CoolCmd]

Visual Studio 2019 has "Horizontal scrolling sensitivity" option, but the extension ignores it. @drewnoakes, you should use this option.