ui: Implement hover color for scrollbar component

[MrSubidubi]

This PR implements color changing for the scrollbar component based upon user mouse interaction.

https://github.com/user-attachments/assets/2fd14e2d-cc5c-4272-906e-bd39bfb007e4

This PR also already adds the state for a scrollbar being actively dragged. However, as themes currently do not provide a color for this scenario, this implementation re-uses the hover color as a placeholder instead. If this feature is at all wanted, I can quickly open up a follow-up PR which adds support for that property to themes as well as this component.

Release Notes:

• Added hover state to scrollbars outside of the editor.