Adds the groundwork needed in order to persist multi-line suggestions,
while providing the parsing strategy which will be reused for the
**Preview** as well.
This is an issue that can only be seen through EE. Further
details can be seen on
https://gitlab.com/gitlab-org/gitlab-ee/issues/9876. In general
we should always use the latest diff version of a file in order
to both create and apply suggestions.
