feat(ui): Initial support for elements appearance prop

[dstaley]

Description

This PR contains the initial implementation of the new API for the elements portion of the appearance prop.

This PR also contains the following sub-PRs:

• test(ui): Add Vitest with in-source testing #4012
• test(ui): Add support for component testing #4015
• feat(ui): Add support for element descriptors #3999

Checklist

• npm test runs as expected.
• npm run build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🐛 Bug fix
• 🌟 New feature
• 🔨 Breaking change
• 📖 Refactoring / dependency upgrade / documentation
• other:

[changeset-bot]

⚠️ No Changeset found

Latest commit: 3c8fbdc

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

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

[dstaley]

these will be removed in the PR that this PR is targeting