[scroll area] Prop to disable custom scrollbars on mobile (iOS/Android)

# Feature request

## Summary

Scroll Area currently disables native scrollbars on mobile, so the styles are consistent everywhere.

On iOS, the Scroll Area's scrollbars lack the rubber band effect (though this could potentially be tweaked given the scroll area component disables it intentionally to fix some issues), and the `transform` updates are pretty laggy on iOS due to heavily async scroll events.

Since mobile scrollbars are already optimized and don't look bad, we can add an option to disable custom scrollbars on iOS & Android specifically.

## Motivation

The scrollbars on the [Dialog examples](https://master--base-ui.netlify.app/react/components/dialog#outside-scroll-dialog) feel worse than the native scrollbars on iOS due to the aforementioned issues (no rubber band, laggy transform updates)