dnd: Introduce a helper to manage the weak pointer
dnd: Introduce a helper to manage the weak pointer

Introduce a setter that takes care of updating the weak ref
whenever we assign info->widget. Just a cleanup of the previous patch.

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