Use UI scaling for the cursor

Issue Description

When interface scale is set, the cursor remains the original size, and doesn't scale with the interface.

Opening PR to fix.

Steps to Reproduce

Set interface scale to 1, view cursor size. Set interface scale to 2, see that cursor remains same size.

System Information

• OpenMW Version: Revision ec82c0fc
• Operating System & Version: MacOS 27
• GPU: M5 Pro
• Morrowind Version: Steam
• Language: English
• Addons: Tribunal, Bloodmoon

Mods

• Are you using mods? No
• Are you using any shader mods? No
• Does it happen in a clean vanilla install? Yes

Logs and Settings