[.NET Migration Guide Revamp] [Phase 1] Move page 'Unavailable technologies'

[StephenBonikowsky]

For details on revamp see: #23561
New TOC: #23215

• Unavailable technologies (MOVE) Move this page and its content to the new TOC location...

• name: Migration guide
  items:

  • name: Overview
    href: ../core/porting/index.md
  • name: General Information
    items:
  • name: Pre-Migration
    items:
    • name: Analyze & Asses the portability of your project
      items:
      • name: Unavailable Technologies
        href: ../core/porting/premigration-analyze-and-asses-the-portability-of-your-project-unavailable-technologies.md

[StephenBonikowsky]

Completed with #24630