cpconverter: Sling-Initial-Content String values are not properly escaped in DocView XML

it seems the cpconverter is not properly escaping string values read from Sling-Initial-Content JSON files and then converting to DocView XML.

in this sample project:
https://github.com/stefanseifert/aem-cloud-service-deployment-issues/tree/feature/archetype-40-DRND-202-escaping
i've introduces in this commit a JSON file in Sling-Initial-Content containing two strings with regexp containing "\". those strings are transferred 1:1 to the DocView XML in the content package, which is wrong. the "\" has to be escaped to be re-read properly via JCR API.

it seems the escaping rules applied by org.apache.jackrabbit.vault.util.DocViewProperty#format are missing.