Full support of multi-project for Security-Code-Scan

What does this MR do?

This MR adds support for multi-solution csharp projects and cleans up the analyzeProject function by reducing complexity, removing extraneous variables, adding some comments, and being more verbose on path variable names.

What are the relevant issue numbers?

gitlab-org/gitlab#281590 (closed)

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
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer