tdf#143104 Fix xlsx import/export of color filter colors
1. In XLSX filter colors are always stored in dxf as foreground
colors, so Calc should keep them, if possible. So practically
use only one color during import.
3. On export we need to distinguish type of filter, this is done
with cellColor=0 or cellColor=1 attribute of <colorFilter>.
4. Since p.1 there is no need to keep on export separate dxf
structures for fg and bg colors: we always use only foreground
color for color filters.
Co-authored-by: Samuel Mehrbrodt <samuel.mehrbrodt@allotropia.de>
Change-Id: Iacd352ae46bf84859dc15ee695b6dc63240afe7d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/122593
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <thorsten.behrens@allotropia.de>