chore: Increases the chart legend horizontal gap

[orangevolon]

Description

• Adds vertical gap between the legend markers when wrapped.
• Replaces the margin-right with gap property.

Related links, issue #, if available: AWSUI-60251

How has this been tested?

• Dev pipeline visual 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 96.44%. Comparing base (76a85a0) to head (0616e8b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3214    +/-   ##
========================================
  Coverage   96.44%   96.44%            
========================================
  Files         790      790            
  Lines       22246    22246            
  Branches     7229     7635   +406     
========================================
  Hits        21455    21455            
+ Misses        784      739    -45     
- Partials        7       52    +45     

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