feat(TreeView): add support for empty parent nodes

[joshblack]

This PR updates TreeView.Item and TreeView.SubTree based on the feedback over in: https://github.com/github/primer/pull/1389#discussion_r998754809

Changelog

New

• Add EmptyDirectory story for TreeView

Changed

• Update TreeView.Item and TreeView.SubTree to coordinate whether or not aria-expanded should be set in sync and async contexts
• Update TreeView.Item to announce when a TreeView.SubTree has no content when used in an async context
• Update TreeView.Item to shift conditional rendering of TreeView.SubTree into TreeView.SubTree
• Update TreeView.test.tsx to remove it.only and replace timers with jest.useFakeTimers

Removed

[changeset-bot]

🦋 Changeset detected

Latest commit: 19a9f0a

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

size-limit report 📦

Path	Size
dist/browser.esm.js	77.99 KB (0%)
dist/browser.umd.js	78.64 KB (0%)

[colebemis]

Looks great! Could you add a couple of tests to make sure the aria-expanded attribute is behaving as expected in the sync and async cases?

[colebemis]

Thanks for tackling this tricky implementation 💖

Should be ready to merge after fixing the lint error.