fix: uui-combobox should correctly handle the active item

[JesmoDev]

This PR Fixes issues with how the combobox handles the active item. Meaning the one that gets highlighted when you navigate with the arrow keys or click an item.
Before the active item was unreliable and not correctly shown visually.

This PR also correctly sets the first item as active when you open the combobox, or make changes to the children, eg. when you search. Example: If you search for "ora" and the first item is orange, pressing space will now pick orange.
Before you would have to click the item, or navigate to it using the arrow keys before pressing enter.

Also adds the expand symbol instead of the custom svg implementation.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (minor updates related to the tooling or maintenance of the repository, does not impact compiled assets)

Checklist

• If my change requires a change to the documentation, I have updated the documentation in this pull request.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[github-actions]

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