Refactor WindowOtherWheelInput to be safer and script window compatible

[AaronVanGeffen]

We've been able to use the mouse scroll wheel to manipulate spinner widgets for years (#7627). However, the function that was added in to support this had not been updated to account for custom (script) windows.

This PR ports the algorithm from OpenLoco/OpenLoco#2019, which is both (memory) safer as well as more accurate, making it compatible with spinner widgets in custom (script) windows.

Fixes Basssiiie/OpenRCT2-RideVehicleEditor#111

[Basssiiie]

I've had a test and ran into a few issues with both plugin spinners and vanilla spinners.

For plugin spinners:

• It works perfect on the text/number part of the spinner, both up and down scroll, except for the fact that the scroll direction is inverted compared vanilla spinners:

	Plugin	Vanilla
Scroll up	Decrement	Increment
Scroll down	Increment	Decrement

• On the [-] button, only scroll up works, not scroll down.
• On the [+] button, neither scroll up or down works.
• When scrolling nearby a dropdown, sometimes glitching occurs, or weird interactions with nearby dropdowns (see pictures below).

For vanilla spinners:

• Scrolling on the text/number part works perfect, both up and down scroll.
• On the [-] button, neither scroll up or down works.
• On the [+] button, only scroll up works to decrement (instead of increment).

(For testing the vanilla spinner I used the park entrance price spinner.)

In this image I tried scrolling on the [+] marked with the red arrow, but it suddenly opened the dropdown below. The dropped down part even opens in the wrong place.

Scrolling this [+] causes a weird vertical bar to show, and sometimes also opens the dropdown.

(Note these dropdown spinners are still a separate dropdown and a separate spinner in full, just overlayed on top of each other.)

[AaronVanGeffen]

@Basssiiie I believe I've addressed the issues with the two latest commits.

Due to how the FlexUI's DropdownSpinnerControl works, the label does not support scrolling, unfortunately. However, the [-][+] spinner buttons work as expected for me.

Adding scrollwheel support to dropdown widgets should be possible as well, though. That will require a new codepath, though, and is therefore best left to another PR.

[Basssiiie]

I've tested it again and I have found no further issues. It all looks good to me now. Thanks!

And yeah don't worry, I don't expect the dropdowns to work here. It's a custom set up anyway and I'm already happy the [+]/[-] now work as expected. 😃