void UnoControl::setDesignMode calls setVisible on the XWindow
so it seems sensible that FmXGridPeer::setDesignMode should
also do so. The desirable side effect is that moving the window
in design mode then is moving a un-shown window so nothing
is invalidated so the paint loop doesn't happen.

Change-Id: Ic5a4ba62590372bec15a29b993b73d6dfb94a8a9
(cherry picked from commit a7816853)
Reviewed-on: https://gerrit.libreoffice.org/19906Reviewed-by: Lionel Elie Mamane <lionel@mamane.lu>
Tested-by: Jenkins <ci@libreoffice.org>
(cherry picked from commit a08a5ff7)