Add Submenu to example apps

[reidbarber]

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

🧢 Your Project:

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-17
• View the storybook-16
• View the documentation

[yihuiliao]

for some reason i can't see the chevrons in the next.js app? seems fine in the cra one tho

[reidbarber]

Weird, and they look fine in the collapsible table.

[reidbarber]

Maybe we can merge the example apps and investigate in a follow-up

[reidbarber]

Looks like it was just due to the Next.js app having box-sizing: border-box; in its styles

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-17
• View the storybook-16
• View the documentation

[rspbot]

## API Changes

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