Changed the easing curve to QEasingCurve::Linear to improve smoothness.
Updated setValue() to prevent restarting the animation unnecessarily if
the new value matches the current target. This change enhances the user
experience by reducing visual jitter and improving animation flow.
Task-number: QTBUG-130307
Pick-to: 6.8
Change-Id: Idd05f17d14a0a653a24a083ad421c3fe0418c3c9
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>