[tabs] Expose tablist scroll overflow state

# Feature request

## Summary

Consumers of tablist don't currently have a way to know whether the list has overflowing content to either ends.

## Examples in other libraries

In `@wordpress/components` we are able to access `ariakit`'s internal state and calculate that information ourselves, and we use it to show a mask gradient


Related code: https://github.com/WordPress/gutenberg/blob/trunk/packages/components/src/tabs/tablist.tsx#L97-L100

## Motivation

Consumers should know whether the tablist has overflowing content in any direction, which could be useful to add visual indication to the user about the overflowing content — for example

- gradient masks to suggest there is more content to scroll
- scroll buttons that could be enabled / disabled

This information could be made available via CSS variables / data attributes on the tablist.

Although I'm not sure how it could be exposed in case it was needed for disabling buttons.

Potentially, we could expose one "variable" per side: inline start, inline end, block start, block end.