Mark final / sealed classes of gtk4
Gtk4 decided that some Classes/Object should be final and can't be subclassed. Currently Gtk4 documentation don't provide a way to discover this information. Only by means of inspecting the source code the
sealed class declaration could be identified.
I would like that Vala and its binding provide some means to make this obvious for the API-Consumers and possible save Programmers some more minutes/hours ;-)