SettingHighlighterPrivate: update highlight on target children changes
It appears there's an issue with the SettingHighlighter when components using it are inside a loader. Reloading or changing content might cause highlighting loss. When the loader is reloaded, the findDescendantItems function does not find the KQuickStyleItem component in childItems, so the highlighting may not work.
The new implementation involves addressing this by updating the target based on the childrenChanged signal.