manage SvXMLImportPropertyMapper with unique_ptr instead of rtl::Reference, which avoids a bunch of ref-counting traffic Change-Id: I1e0e95408cdd5dc4271fa72178e57087737eb062 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/183751 Tested-by: Jenkins Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>