GtkDialog: Be a little more careful about button placement
GtkDialog: Be a little more careful about button placement

We were applying response based heuristics, even if the button
is explicitly put in the headerbar. That broke button placement
in some epiphany dialogs, such as the Cookies one. Therefore,
restrict the heuristics to action widgets that are added through
gtk_widget_add_action_widget() or <child type="action">, where it
is not possible to specify placement explicitly.

Adamovskiy/gtk,Lyude/gtk-,jessevdk/gtk,jigpu/gtk,jadahl/gtk,jadahl/gtk,jessevdk/gtk,grubersjoe/adwaita,jadahl/gtk,jessevdk/gtk,davidgumberg/gtk,Lyude/gtk-,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,alexlarsson/gtk,jigpu/gtk,chergert/gtk,ahodesuka/gtk,jessevdk/gtk,Adamovskiy/gtk,alexlarsson/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,Lyude/gtk-,ahodesuka/gtk,Lyude/gtk-,chergert/gtk,alexlarsson/gtk,grubersjoe/adwaita,davidgumberg/gtk,grubersjoe/adwaita,Adamovskiy/gtk,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,Adamovskiy/gtk,jigpu/gtk,davidgumberg/gtk,chergert/gtk,davidgumberg/gtk,jigpu/gtk,Lyude/gtk-,jadahl/gtk,ahodesuka/gtk,alexlarsson/gtk,alexlarsson/gtk,chergert/gtk,Lyude/gtk-,davidgumberg/gtk,Adamovskiy/gtk,grubersjoe/adwaita,chergert/gtk,alexlarsson/gtk,Adamovskiy/gtk,jadahl/gtk,grubersjoe/adwaita,ahodesuka/gtk,ahodesuka/gtk,chergert/gtk,ahodesuka/gtk,Lyude/gtk-,jessevdk/gtk,Lyude/gtk-,jessevdk/gtk,davidgumberg/gtk,davidgumberg/gtk,jadahl/gtk,jadahl/gtk,ahodesuka/gtk,jessevdk/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,ahodesuka/gtk,jigpu/gtk,grubersjoe/adwaita