Fix: vehicle-cursor size-limit did not account for the interface zoom level. #8739
Motivation / Problem
When dragging vehicles in depot, the vehicles being dragged are used as mouse cursor.
Thus OpenTTD enforces a maximum length for vehicles as mouse cursor, and then cuts the vehicle.
This PR scales the cursor size limit by the interface zoom level.
Checklist for review
Some things are not automated, and forgotten often. This list is a reminder for the reviewers.