Added wxDataViewEvent::SetDragFlags() and GetDropEffect() methods.

Allow specifying the drag operation flags and retrieving the drop effect when
it's over for wxDataViewCtrl drag-and-drop.

Currently this is only implemented in the generic version.

Closes #12583.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71324 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dataview/dataview.cpp

@@ -841,6 +841,7 @@ void MyFrame::OnBeginDrag( wxDataViewEvent &event )
     wxTextDataObject *obj = new wxTextDataObject;
     obj->SetText( node->m_title );
     event.SetDataObject( obj );
+    event.SetDragFlags(wxDrag_AllowMove); // allows both copy and move
 }
 
 void MyFrame::OnDropPossible( wxDataViewEvent &event )