oox: import WPS shape with text as shape with textbox

This allows having real shapes (like having rounded corners) and complex
content (like containing a table) at the same time.

WPS shapes are wrappers around drawingML markup in DOCX files, so this
only affects the DOCX import.

Change-Id: Iad1c1c61233be1c17efa1821e680927aa9587215