[scroll area] Add `ScrollArea.ScrollButton` component

# Feature request

## Summary

A component that becomes visible when Scroll Area's content is overflowing at the start or the end (or both).

The component could accept props such as:

- whether it should target content overflowing at the start or the end of the container (this can also be implemented as two separate components)
- a scroll target for when the button is clicked (defaults to `0` for start, `scollHeight` for end)

## Examples in other libraries

Not another library per se, but this pattern can be found in Slack:


## Motivation

This component can be useful when it's important to give end users a strong (actionable) visual hint about there being more hidden (overflowing) content.

This pattern can be currently implemented in consumerland similarly to what descripted in #2444