Enforce using the latest diff version when creating suggestions

What does this MR do?

This enforces the usage of the latest diff file content when creating suggestions. This is a bugfix of an issue that can just be seen through EE when publishing outdated draft notes. In general, we were using the note.original_position, which points to an outdated version of the MR, thus fetching an outdated blob of a file, which leads to creating an unexpected suggestion diff when publishing the review.

Further details of the issue can be seen on https://gitlab.com/gitlab-org/gitlab-ee/issues/9876.

Ideally we should manage to work on https://gitlab.com/gitlab-org/gitlab-ee/issues/8823 to fully support suggestions on draft notes.

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/9876

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer