Fix Linux Piu wheel scrolling

[meganetaaan]

Summary

Fix mouse wheel scrolling in Linux Piu applications.

Linux GTK scroll events produced scrolling that was both reversed and much smaller than on other platforms. This change normalizes the direction and amount to match the behavior of the Windows and other Piu backends.

Testing

• Built xsbug for x-lin.
• Built mcsim for x-lin.
• Verified wheel scrolling direction and speed in xsbug on Sway/Wayland.

[phoddie]

Nice. There is so much variability in Linux, I wonder if this change will work well across distributions. There's only one practical way to find out.... merging it. ;) So, we'll do that.

Thank you!

[mkellner]

This is merged and will be available in the next release. Thank you.