fix: Remove underline from trailing whitespace in external links

[xyos]

Description

Removes the non-breaking space that caused underlines to appear below trailing whitespace between external icon and link text. Replaces it with margin-inline-start.

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

How has this been tested?

I tested the link permutation page at http://localhost:8081/#/light/link/permutations manually and generated a diff to check difference between changes and previous implementation using odiff:

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 96.99%. Comparing base (da6e199) to head (ad348b7).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3709    +/-   ##
========================================
  Coverage   96.99%   96.99%            
========================================
  Files         820      820            
  Lines       23799    23799            
  Branches     7917     8338   +421     
========================================
  Hits        23084    23084            
  Misses        709      709            
  Partials        6        6            

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[avinashbot]

@xyos Hi! Thanks for opening the pull request, taking a closer look and running a full screenshot comparison test.

Though there is one regression that should be addressed. Being the one who made the original change with the  , the issue that I was fixing was that the external icon would sometimes wrap into the next line on its own, and it wasn't ideal to have an icon just hanging out on a new line like that. You can see the issue on the #/light/link/icon-overflow-permutations dev page (current state on the left, this PR on the right).

I recall trying to do the \a0 pseudoelement trick, but it didn't quite work for me. But perhaps there's a way of making it work with a little bit more experimentation?