Default scroll behavior is non-natural

[Deftu]

My existing fix in 114f9dd is extremely sub optimal as it bandaids a fix into the PolyUIScreen rather than fixing the actual behavior.

As it is now, the default value of "natural scrolling" is set to true, which inverses the scroll direction so that up-scroll moves downwards and vice versa, which is unnatural for most non-Mac users.
The scroll amount is also unnatural and needs to be looked into, as GLFW in 1.13+ (1.16+ for us) provides a delta of 1.0/-1.0 (on mice, at least), meaning we'd only move 1 pixel per step on those versions, and LWJGL's input handler in 1.12- provided ~120 (for me, I assume it's based on system settings), which seemed to equate to 120 pixels.

My fix forcibly undid natural scrolling mathematically and forced scrolling to move 15 pixels per step.

[nextdayy]

This is a limitation of the Minecraft scrolling system. on 1.12-, we can't get accurate scrolling for trackpads or based on system settings - LWJGL2 just doesn't have an accurate scrolling setup. on GLFW, the minecraft method returns the value 1 or -1, but we could potentially get the raw scroll value from the GLFW using a mixin into the callback.
The natural scrolling can be controlled by PolyUI.settings.naturalScrolling. also see PolyUI/GLFWWindow.kt#L266-275 for "automatic" detection.