Port gdk_pixbuf_new_from_stream_[at_scale_]async to GTask
Port gdk_pixbuf_new_from_stream_[at_scale_]async to GTask

https://bugzilla.gnome.org/show_bug.cgi?id=712704

YueLinHo/MB3Gdk-pixbuf,Distrotech/gdk-pixbuf,GNOME/gdk-pixbuf,YueLinHo/MB3Gdk-pixbuf,YueLinHo/MB3Gdk-pixbuf,GNOME/gdk-pixbuf,Distrotech/gdk-pixbuf,Distrotech/gdk-pixbuf,GNOME/gdk-pixbuf,Distrotech/gdk-pixbuf,GNOME/gdk-pixbuf,YueLinHo/MB3Gdk-pixbuf,YueLinHo/MB3Gdk-pixbuf,Distrotech/gdk-pixbuf