[.NET Migration Guide Revamp] [Phase 1] Move .NET Upgrade Assistant tool content

[StephenBonikowsky]

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

• .NET Upgrade Assistant tool (MOVE) Move as is to the following toc location...

• name: Migration guide
  items:

  • name: Overview
    href: ../core/porting/index.md
  • name: General Information
    items:
    • name: .NET Upgrade Assistant tool
      items:
      • name: Overview
        href: ../core/porting/upgrade-assistant-overview.md
      • name: Windows Presentation Foundation
        href: ../core/porting/upgrade-assistant-wpf-framework.md
      • name: Windows Forms
        href: ../core/porting/upgrade-assistant-winforms-framework.md
      • name: ASP.NET Core
        href: ../core/porting/upgrade-assistant-aspnetmvc.md

[StephenBonikowsky]

Completed with #24630