Add some API to O*StringLiteral, to make it easier to use in some places that were using O*String Change-Id: I1fb93bd47ac2065c9220d509aad3f4320326d99e Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100270 Tested-by: Jenkins Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>