places sidebar: Preserve ::populate-popup functionality
places sidebar: Preserve ::populate-popup functionality

We "fix" this signal the same way we did for GtkEntry and
GtkTextView: slightly change the signature so that the passed
widget may be a container other than a GtkMenu, and add a
property to explicitly opt in to receiving the signal in
this case.

grubersjoe/adwaita,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,jadahl/gtk,Adamovskiy/gtk,chergert/gtk,chergert/gtk,jigpu/gtk,Adamovskiy/gtk,davidgumberg/gtk,alexlarsson/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,jigpu/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jigpu/gtk,grubersjoe/adwaita,alexlarsson/gtk,davidgumberg/gtk,grubersjoe/adwaita,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,jadahl/gtk,Adamovskiy/gtk,jadahl/gtk,Adamovskiy/gtk,jadahl/gtk,grubersjoe/adwaita,chergert/gtk,chergert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,alexlarsson/gtk,chergert/gtk,chergert/gtk,davidgumberg/gtk,davidgumberg/gtk,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,jigpu/gtk,jadahl/gtk