[ScrollArea] Viewport fixes

[vladmoroz]

• Fix asChild prop not working as expected on the Viewport part
• Rework the inner content element styles on the Viewport part
  • Replace display: table with flex styles on the parent that allow the viewport to fill container height (based on the Radix Themes implementation)
  • Replace most related inline styles with 0,0,0 specificity styles for easier overrides via [data-radix-scroll-area-content]
  • Fix text-overflow: ellipsis not working when used with a vertical scrollbar

Closes #926 #1666