SettingsExpander not showing title and description on Wasm/Uno

The SettingsExpander is not showing title or description when running on Wasm.

_Originally posted by @lukasf in https://github.com/CommunityToolkit/Windows/discussions/383#discussioncomment-8987733_

> Second issue I noticed: SettingsExpander is still not working on any Uno targets: The header and icons are not shown. The control can be expanded and content is shown, but the header is completely empty.
>
> You can also see this here: https://toolkitlabs.dev/
>
> This was also the case in all older Uno WCT builds, so it is not a new bug. But since you now officially support Uno from WCT 8, it would be great if you can look into this.

Start by reproducing SettingsExpander on a Wasm/Uno target and inspect the control's implementation and existing tests, if present. Trace why the title, description, header, and icons are absent while expansion content works; done means these elements render correctly on the affected Uno targets.

Written by the indexing model from the issue text.