sw: export fieldmark of postit fields if possible
sw: export fieldmark of postit fields if possible

This way the UNO export filters won't have to remind if the postit field
had an associated fieldmark or not, but can just query the fieldmark
type and ignore e.g. comment fieldmarks.

Change-Id: I791b07fd371f57ec35d8309e666058237dadf190

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core