fdo#80742 RTF filter: import RTF_OUTLINELEVEL

(cherry picked from commit c3657be928732f1b3b3b238f625de304a90a1ae1)

Change-Id: I49d94bd72af610e88128cd405e4786d2e9ba65ed
Reviewed-on: https://gerrit.libreoffice.org/10727
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>