fix: Remove underline from trailing whitespace in external links

[avinashbot]

Description

Resurrecting a contribution in #3709 that neither I nor the contributor could find a path forward for. While spending time investigating a fix for #4496, I discovered a trick that lets us do this without a space (apparently this character existed for many years now, just hadn't come across it until just now).

Keeping the original commit in there to maintain the attribution to the original contributor who kicked it off.

Related links, issue #, if available: AWSUI-60840

How has this been tested?

Would definitely show up in screenshot tests.

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 97.41%. Comparing base (16e2159) to head (e70fa80).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4497   +/-   ##
=======================================
  Coverage   97.41%   97.41%           
=======================================
  Files         933      933           
  Lines       29595    29595           
  Branches    10757    10756    -1     
=======================================
  Hits        28831    28831           
- Misses        716      757   +41     
+ Partials       48        7   -41     

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