Clean up Top-Level exports

[FabianLars]

As mentioned here: #14009 it's getting quite crowded and maybe we should organize it a bit more. Again taking 14009 as an example, all the dpi re-exports could be a exported similar to utils/http.

Another example, we already have webview and window modules but have quite a view webview / window exports on the top level as well eg WebviewEvent and WebviewUrl

[WSH032]

Ref #14013

Also, I feel that TitleBarStyle should be exported under mod window (instead of the top-level module), similar to how window::ProgressBarState is handled, since it's only used for Window::set_title_bar_style.

I propose that TitleBarStyle should also join this party 🤓