Factor out the setFilterPropsFromFormat() also used by
SwVbaDocument::SaveAs2000() to a header file of its own.

Change-Id: I4bc9e1e420719a115036beb7e82a4ac3feac05f0
Reviewed-on: https://gerrit.libreoffice.org/70980
Tested-by: Jenkins
Reviewed-by: Tor Lillqvist <tml@collabora.com>