interface → SV: correctly marshal class struct args of functions
interface → SV: correctly marshal class struct args of functions

Class structs were already handled correctly when they are instance args of
methods.  Extend the special treatment to function args.  Occurs, e.g., with
GooCanvas::CanvasItem::class_list_child_properties.

GNOME/perl-Glib-Object-Introspection,cpanxaoc/perl-Glib-Object-Introspection,cpanxaoc/perl-Glib-Object-Introspection,GNOME/perl-Glib-Object-Introspection