rather than toplevel. This avoid the problem under wayland where
with an initially maximized calc clicking in it will select all
cells from 0,0 to the clicked cell until the mouse is released

Change-Id: I138fe587c9cb7cfff0293847c00730593e3244e1
Reviewed-on: https://gerrit.libreoffice.org/61087
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>