[client] Extend Registry by providing name and version of announced interfaces

This change addresses the sometimes cumbersome to use API of Registry.
So far to bind an interface one needed to connect to the signals when
setting up the registry. There was no other way to get the name and
version at a later point. This made it difficult to use one Registry
in different parts of an Wayland application.

This change adds a convenient:
struct AnnouncedInterface { quint32 name; quint32 version;};
AnnouncedInterface interface(Interface) const
QVector<AnnouncedInterface> interfaces(Interface) const

The first one is meant for interfaces like wl_shm which is normally only
announced once. The latter one is meant for interfaces like wl_output
for which normally multiple interfaces can get announced.

Those methods can be used without having to connect to the announced
spy.

REVIEW: 124734