feat: Make color background segment wrapper public

[SpyZzey]

Description

• Add colorBackgroundDropdownItemSelected token for selected dropdown item backgrounds (select, multiselect, autosuggest, datepicker)
• Add colorBackgroundSegmentWrapper token for segmented control wrapper background
• Add colorTextDropdownItemSecondary token for secondary text in dropdown items (descriptions, tags)
• Add colorTextIconSubtle token for subtle/secondary icons with lower visual emphasis

All new tokens are marked public and themeable.

Related links, issue #, if available: n/a

How has this been tested?

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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 (3417c05) to head (4ca1e9d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4483   +/-   ##
=======================================
  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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