ui: Clean up `PlatformTitlebar` implementation (#9413)

This PR cleans up the implementation of the `PlatformTitlebar` component
to better match our conventions for building UI components.

Release Notes:

- N/A
123d3ee282Marshall Bowers committed on 3/15/2024, 6:31:02 PM· committed by GitHubparentdb43479
5 files changedLine totals unavailable