fix(#1999): Improve accessibility in DocSearch results

[majornista]

Update to adobe#2016 to improve accessibility in DocSearch results so that they better implement the WAI-ARIA ComboBox design pattern.

• Fixes a few other docs issues identified with aXe DevTools.
• Fixes a couple console error messages with themeSwitcherButton and hamburgerButton.

Relates to adobe#1999 and adobe#2016

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue 1999.
• 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:

1. yarn start:docs
2. Open http://localhost:1234/
3. Start screen reader, like VoiceOver.
4. Navigate to Search combobox.
5. Enter some text to search.
6. Use arrow down/up to navigate through search terms in dropdown.
7. Verify that option items announce without double voicing redundant content when subcategory matches suggestion title.

🧢 Your Project:

Adobe/Accessibility

Related issue:

algolia/docsearch#1014

[solimant]

Thank you 👍🏼

[majornista]

Issue filed with Algolia: algolia/docsearch#1014