USWDS-Site: Add search accessibility tests page

[mahoneycm]

Summary

Added accessibility tests page for the search component.

[!Important] We should update changelog dates before merging.

Related issue

Closes #2626

Preview link

• Search accessibility checklist page →
• Search component page →

Resources

• Creating accessibility checklists process doc (Google docs 🔒)
• Accessibility checklist spreadsheet (Google sheets 🔒)

Testing and review

1. Confirm that both the main component page and the accessibility tests page have the correct compliance tag at the top.
2. Confirm that the main component page links to the accessibility tests page in the side navigation.
3. Confirm that the main component page links to the accessibility tests page from the accessibility guidance section.
4. Confirm that the main component page shows the accessibility tests summary.
5. Check that accessibility tests page provides the correct counts for each test status type.
6. Confirm the test checklist summaries and data are accurate.
7. Confirm new 3.2.3 wcag criterion is accurate and link works
8. Confirm no visual issues.
9. Confirm there is an appropriate changelog entry on both the main component page and the accessibility tests page.

[mahoneycm]

@sarah-sch Thanks for making those changes! I updated the focus indicator summary to match your recommendation and it's ready for you re-review!