fix: Make navigable group core-only

[jperals]

Description

For the system tag to be extracted by Documenter, the comment needs to be above the export statement.

How has this been tested?

• Updated the snapshot with npm run build && npx jest -c jest.unit.config.js -u src/__tests__/snapshot-tests/documenter.test.ts (part of this PR diff)
• Building the change in my website pipeline to make sure the website doesn't break: 7609312490

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.12%. Comparing base (0c4c33e) to head (0c3c5b7).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4063   +/-   ##
=======================================
  Coverage   97.12%   97.12%           
=======================================
  Files         863      863           
  Lines       25294    25294           
  Branches     9119     9119           
=======================================
  Hits        24566    24566           
  Misses        722      722           
  Partials        6        6           

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