[dialog] Internal api exposed by handle

# Bug report

## Current behavior

I can access api such as `handle.store.useState('activeTriggerId')`

## Expected behavior

I'm not really complaining, but I'm guessing this might not be intentional :-)

## Reproducible example

https://stackblitz.com/edit/vitejs-vite-uk2kkefj?file=src%2FApp.tsx,package.json,node_modules%2F%40base-ui%2Freact%2Fnode_modules%2F%40base-ui%2Futils%2Fesm%2Fstore%2FReactStore.d.ts
## Base UI version

For example v1.2.0

## Which browser are you using?

Chrome

## Which OS are you using?

macOS

## Which assistive tech are you using (if applicable)?

n/a

## Additional context

This likely applies to other components with handles. If this _is_ intentional, that would be good to know because some of this api might come in handy. I'm mostly looking for clarity on if using this api is supported/expected or not.