oox: handle textboxes in ShapeContextHandler::endFastElement()

DOCX shape import normally works by oox creating the shape, then
writerfilter handling the shape text. For drawingML shapes, having shape
text, this a bit more complicated, as there are shape properties after
the shape text as well.

ShapeContextHandler::endFastElement() assumed that shape text is only
possible on css.text.TextFrame shapes: also handle shapes having a
TextBox as well.

sw/qa/extras/ooxmlimport/data/mce-nested.docx is a reproducer for this
problem (group shape missing), when TextBoxes are enabled by default in
oox.

Change-Id: I7a412b31965cf363da0b0c7fcc732741f2037542