The plan:

1. As Regina points out, there is already (in ODF 1.2, but not ODF 1.1)
   a style:shrink-to-fit attribute for shapes, so use this to represent
   the AUTOFIT value.

   The fallback from AUTOFIT to draw:fit-to-size="true" was a stupid
   idea anyway, probably "false" is less annoying in practice.

   There are 2 different shapes that implement TextFitToSize property:

   a) text shapes already interpret ALLLINES and PROPORTIONAL exactly
      the same
   b) fontwork custom shapes interpret ALLLINES but do nothing for
      PROPORTIONAL

   As Regina points out, there is no shape that needs to distinguish
   between ALLLINES and PROPORTIONAL, so we do a minor behavioral
   API CHANGE and from now on interpret PROPORTIONAL as ALLLINES
   on fontwork custom shapes.  This obviates the need to distinguish
   the values in ODF and so we don't need a new attribute,
   just use draw:fit-to-size="true" for both.

   On import, use MID_FLAG_MERGE_PROPERTY to combine the 2 attributes
   into one value.

2. Restrict the export of draw:fit-to-size to only the standard
   values "true"/"false".

This implements step 1, the step 2 will be done in the future when
most users have the import of the style:shrink-to-fit.

Change-Id: I4a378aa110fdb82db7a99a839d7ff207248a73e7
Reviewed-on: https://gerrit.libreoffice.org/43521Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>