There are two cases here: if the shapes contain tables (or other
Writer-specific features), we should use text frames and we should not
create the actual group shape, as Writer textframes can't be part of
such group shapes.  The other case is when the shapes contain simple
text, OTOH there are groupshape-level transformations defined, in that
case we should choose drawinglayer rectangles and actually create a
group shape.

This commit implements support for the first case only.

Change-Id: I9dc99b0711ce5c7a29ea0b14539df0121f9de3d0