Scrollbar fixes

[niels9001]

Updated the (Dynamic)ScrollBar default style to be more inline with WinUI addressing: #872

• Added on hover background color (couldn't use InAppAcrylicDefaultBrush like in WinUI, but used the replacement color we also use for e.g. Flyout)
• Decreased scrollbar thumb width based on WinUI spec
• Decreased icon fontsize so it's centered and inline with WinUI spec

Before:

After:

ScrollBar now overlaps content, addressing: #871

• Tweaked the default ScrollViewer style so it overlaps its content
• Set a default style for PassiveScrollViewer so it uses the ScrollViewer style as well (as ListView uses PassiveScrollViewer)
  Before:
  

After:

[niels9001]

@pomianowski In case this PR gets approved, would you mind creating a Preview.13 :)?