UI: Deselect other objects when dragging into 3D View

When dragging an object into the 3D View, e.g. from the Outliner or the Asset
Browser, other objects wouldn't get deselected. That differs from what other
drop operations do, which create a new object. They deselect other objects in a
lower-level function, which happens to not be called for just dropping objects.
So I guess this is an oversight.
Old behavior was also a bit annoying because users seem to expect this to
deselect.

source/blender/editors/object/object_add.c

@@ -3364,6 +3364,9 @@ static int object_add_named_exec(bContext *C, wmOperator *op)
     ED_view3d_cursor3d_position(C, mval, false, basen->object->loc);
   }
 
+  /* object_add_duplicate_internal() doesn't deselect other objects, unlike object_add_common() or
+   * BKE_view_layer_base_deselect_all(). */
+  ED_object_base_deselect_all(view_layer, NULL, BA_DESELECT);
   ED_object_base_select(basen, BA_SELECT);
   ED_object_base_activate(C, basen);