fdo#74230: ODF export: write stroke and fill color in graphic defaults

The pool defaults for svg:stroke-color and draw:fill-color were changed
and while previously (effective, manually overridden) defaults were
written into ODF files, this was lost with the change; restore that.

(regression from c0eb5e7772c848806db8ab461f77f9549c1d8b2b)

Change-Id: Ibcd863260976aa42116175c7f19cb33760af986f
(cherry picked from commit 45d3577bc5726eee44f491fd30a7f11dc428431a)
Reviewed-on: https://gerrit.libreoffice.org/7929
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>