Add configurable scrollbar thickness

[gilleslabelle]

Summary
Please add support for configurable scrollbar thickness for the scrollbars managed by this package.

Current behavior
The package can keep scrollbars expanded, but it does not seem to provide a way to control the width (vertical and horizontal). The original size is very thin so having the possibility to resize it would be great.

This would help for:

• accessibility
• touch-friendly UI
• cases where the default WinUI scrollbar is too narrow to grab comfortably

Thanks a lot.