This patch analyses DXF version data to heuristically detect
which files use OEM text encoding (DOS versions of AutoCAD).
Also, it uses LO's currently-selected default document language,
instead of system locale, so that user can change that to match
language of the DXF, and get correct result.

Change-Id: I3aec7e24f3d7efca35d0dd1acca8b277a076f210
Reviewed-on: https://gerrit.libreoffice.org/28556Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>