Create sarif package and expose structs and functions

What does this MR do?

This MR creates a new sarif package and exposes certain fields needed by GitLab analyzers. See this discussion for details.

What are the relevant issue numbers?

Distill sast-ide branch down to include the bar... (gitlab-org/gitlab#478877 - closed) • Julian Thome • 17.4

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Ensure the report version matches the equivalent schema version
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer