Ability to override app theme across all system UI (title bar, Share dialog, file picker, etc)

Today many Windows apps provide an option to use a different one than the default. However, there have been some challenges with that for example:

1. System provided UI will still use the system theme (some things like the Share dialog provides the ability to customize the theme it uses but not everything).
2. Unless you use a custom title bar, the default title bar will use the system theme and not the theme for the application, this is where many bugs happen since many don't bother.
3. Third-party libraries need to ask the application the theme or assume the app theme is the same as the default system theme.

Consider adding an API where the application can set whether it wants light, dark and Windows default and UI frameworks will automatically adapt it as well as all the system UI including default title bar.