use those for drag operation start in Qt5Widget and eventually
to construct DropTargetDragEnterEvent

Change-Id: I3a92cbe722dadc64f8a210f7fd4016c8eb17216b
Reviewed-on: https://gerrit.libreoffice.org/68675
Tested-by: Jenkins
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>