Fix Submenu Tray experience for iOS VoiceOver

[reidbarber]

Due to the submenu tray animation, sometimes the parent menu would stay focused when the submenu opened on iOS when using VoiceOver. By focusing the first item after the animation completes, we can avoid this issue.

✅ 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:

Test submenu tray experience in iOS with VoiceOver.

🧢 Your Project:

RSP

[rspbot]

Build successful! 🎉

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

[devongovett]

A bit hacky 😜, but it seems to work pretty well in VO on my device.

[rspbot]

Build successful! 🎉

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

[rspbot]

## API Changes

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