Inspired by a recent bug report where we were assigning the result
of VclPtr<T>::Create to a raw pointer.

As a consequence, we also need to change various methods that were
returning newly created Window subclasses via raw pointer, to
instead return those via VclPtr

Change-Id: I8118e0195a5b2b4780e646cfb0e151692e54ae2b
Reviewed-on: https://gerrit.libreoffice.org/31318Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>