"auto" means viewing application decides what the size/dimension
is going to be i.e. act as if no particular size was provided

Also use metric dimensions from bitmaps if available.

Change-Id: Ic3860ecad0c4e1c2b7f6131c03c6612241a20c7c
Reviewed-on: https://gerrit.libreoffice.org/52404Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>