Implement initial useDisclosure hook

[joshblack]

As part of our work on disclosure, we would like to start out by building a useDisclosure hook that encapsulates the disclosure design pattern from WAI-ARIA.

This hook should:

• Return the props necessary for the button and content parts of a disclosure pattern
• Should be used in an unstable_Disclosure story as an example
• Include tests to verify that the behavior matches the keyboard interaction and WAI-ARIA Roles/States/Properties required by the pattern