Replace MouseScrollUnit::SCROLL_UNIT_CONVERSION_FACTOR with a Resource

[stevehello166]

Objective

Fixes #24508

Solution

Replace MouseScrollUnit with a Resource of the same name and remove it from the structs and events related to scrolling. More work still needs to be done to make sure that the value in MouseScrollUnit is actually respected

Testing

• Running standard test suite/ci as well as related examples to make sure that they haven't broken

[alice-i-cecile]

@MyCodingSpace5, take a look at this PR and how it evolves :) It should make clear what I meant by a resource here, and how work is done in open source.

[amtep]

I think the idea is to insert a conversion factor as a resource, one that users can look up instead of the constant SCROLL_UNIT_CONVERSION_FACTOR.

It can start out equal to that constant; adapting it to the platform is for later work.

[stevehello166]

Alright, I reverted the previous changes and added MouseScrollPixelsPerLine resource. I'm not entirely sure about the name of the resource given it's length. However, it is more descriptive than SCROLL_UNIT_CONVERSION_FACTOR.

[alice-i-cecile]

That's a totally fine name: I don't think this will come up often.

[alice-i-cecile]

Looking good, but I think we can add a couple helper methods and make this much nicer :)

[amtep]

Some confusion around to_lines and to_pixels, otherwise looks good :)