📌 Feature Request: Show Solution-Level Files (e.g., README.md) in Solution Explorer

Originally posted by @awlc at https://github.com/dotnet/vscode-csharp/issues/8454

📝 Summary
Enable Solution Explorer in Visual Studio Code (and optionally Visual Studio) to display solution-level files—such as README.md, .editorconfig, or .gitignore—that reside in the root folder of a .sln file but are not part of any individual project.

🔍 Problem
Currently, Solution Explorer only shows files that are explicitly included in .csproj or .sln files. This excludes important documentation and configuration files that are meant to serve the entire solution. For example, a top-level README.md provides essential context for contributors and developers, but it remains invisible in Solution Explorer unless manually added to a project.

🎯 Why It Matters

• Improves visibility of solution-wide documentation
• Aligns with best practices for multi-project solutions and open-source repositories
• Reduces confusion for developers who rely on Solution Explorer as their primary navigation tool
• Encourages proper organization of solution-level assets

✅ Proposed Solution
Introduce a “Solution Root” node in Solution Explorer that:

• Displays all non-project files in the solution directory
• Optionally allows toggling visibility via settings
• Does not require modifying .csproj files
  💬 Additional Notes
  This feature would be especially helpful in Visual Studio Code with the C# extension, where the Solution Explorer is often the default view for navigating .NET solutions.

No implementation files, tests, or entry points are identified in the report. Start by reviewing the existing Solution Explorer behavior and the proposed Solution Root requirements. Done means solution-level files such as README.md, .editorconfig, and .gitignore are discoverable without adding them to a project, with the visibility behavior and settings defined.