VideoPlayerViewController: Update brightness utility

This update improves brightness management to deliver a smoother and more intuitive experience:

• Preserve System Brightness: This fixes an issue where the system brightness could unexpectedly change after opening the Control Center, ensuring it remains consistent unless intentionally adjusted. This issue could occur if the brightness was modified using the brightness control view and the Control Center was then opened.

• Ensure Smooth Brightness Control: Fixes the functionality of the brightness control view, allowing it to respond accurately to adjustments made directly from the Control Center.

• Separate Brightness Levels: It separates the system brightness from the brightness value used by video players, preventing conflicts and ensuring that the system brightness is restored when exiting the app or closing the video player.