GtkFileChooserWidget using wrong signatures for ::drag-begin and ::drag-end

GtkFileChooserWidget connects to ::drag-begin and ::drag-end, but takes a GdkDrop instead of a GdkDrag[0][1]. That is passed along to gtk_places_sidebar_set_drop_targets_visible()[2], which takes a GdkDrop. Now, all is fine and dandy until one connects to GtkPlacesSidebar::drag-action-requested, which takes a code path that just forwards the GdkDrop from gtk_places_sidebar_set_drop_targets_visible()[3].