feat: make dropdown component public

[mxschll]

Description

• Exposes the internal dropdown component and refactors existing components/pages to use public version.
• Introduces test utils for dropdown.
• Adds style api to dropdown.

Related links, issue #, if available: RGJgABPXohP8

How has this been tested?

Changes went through the pipeline without visual regressions.

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 97.45%. Comparing base (3189432) to head (470d83a).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4345   +/-   ##
=======================================
  Coverage   97.45%   97.45%           
=======================================
  Files         902      905    +3     
  Lines       26451    26506   +55     
  Branches     9530     9553   +23     
=======================================
+ Hits        25777    25832   +55     
  Misses        631      631           
  Partials       43       43           

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[jperals]

Is this necessary since the entire component is Core-only anyway?

[mxschll]

I'd leave it here for the sake of consistency, as well as for future use in case we want to expose the component to the console (probably unlikely), so we can keep the style API core only. Or is this concern unjustified?

[jperals]

Not blocking, as this doesn't break anything

[jperals]

Why are the properties actually nested under dropdown? Is it because there is also the trigger, although we don't consider styling it for now?

[mxschll]

Yes, I wanted to go with root initially but that's also not ideal as we need to style the :after element which is used to display the border as well as the dropdown wrapper to change border radius and background. So I grouped it in dropdown. Since the trigger is custom, we probably could remove this nesting entirely...

[jperals]

Not blocking, as this doesn't break anything