Use `aria-modal` in dialogs

# Feature request

## Summary

`aria-modal` is a more modern alternative

## Examples in other libraries

React Spectrum uses aria-modal (with an optional [polyfill](https://github.com/adobe/react-spectrum/tree/092229c62c070e6405d4b6d74bb27f328508e781/packages/%40react-aria/aria-modal-polyfill))

## Motivation

Using `aria-modal` should present a better UX for users using browser/screen readers that support this property compared to adding `aria-hidden` to elements outside the dialog.