We should add a new writable Ti.UI.overrideUserInterfaceStyle property that allows you to force the app to use a dark or light theme instead of using the system assigned theme. If this property is assigned the Ti.UI.USER_INTERFACE_STYLE_UNSPECIFIED constant (the default), then the app will use the system theme instead.
The existing read-only Ti.UI.userInterfaceStyle property needs to be its own property. If the overrideUserInterfaceStyle is set to unspecified, then the userInterfaceStyle property will reveal if the system is using the dark or light theme.
On iOS, this can be implemented via the native UIView.overrideUserInterfaceStyle property.
On Android, this can be implemented via the Java AppCompatDelegate.setNightMode() method.