[combobox] Add `autoHighlight` prop

[atomiks]

Feature request

Autocomplete accepts an autoHighlight prop, but not Combobox.

Summary

Linear's priority combobox automatically highlights the first item when filtering so you only have to press Enter, not ArrowDown + Enter — #2630

[github-actions]

This feature will be available in the next npm release of Base UI.

In the meantime, you can try it out on our Canary release channel:

npm i https://pkg.pr.new/@base-ui-components/react@2668