fix(modals): provide ref object for focusvisible

[hzhu]

Description

It was recently discovered that focusvisible behavior broke within modal components.

Detail

It looks like the environment changes when the modal is mounted but the change is not captured by the useFocusVisible hook.

In order to capture this change, the environment is passed to useFocusVisible as the relativeDocument. A useEffect within useFocusVisible re-runs the effect accordingly when the relativeDocument is updated.

🙏 Thanks @Austin94 for helping figure out the root problem.

Screenshots

Before:

After:

Checklist

• 🌐 Styleguidist demo is up-to-date (yarn start)
• ⬅️ renders as expected with reversed (RTL) direction
• 🤘 renders as expected with Bedrock CSS (?bedrock)
• ♿ analyzed via axe and evaluated using VoiceOver
• 💂‍♂️ includes new unit tests
• 📝 tested in Chrome, Firefox, Safari, Edge, and IE11

[coveralls]

Coverage increased (+0.0009%) to 95.834% when pulling c7ffc2c on hzhu/modal-focusvisible into 08616ae on main.