gdbus-codegen: Tag interfaces and properties so annotated with G_PARAM_DEPRECATED
If a D-Bus interface or one of its property is annotated with
org.freedesktop.DBus.Deprecated, then the corresponding GObject properties were not being marked with
G_PARAM_DEPRECATED, even though the gtk-doc snippet had the 'Deprecated: ' tag.
G_PARAM_DEPRECATED is older than
gdbus-codegen, 2.26 and 2.30 respectively, hence it can be used unconditionally.