Add C#/.NET language support (pending tooling maturity)

[richardkiene]

Summary

Add C#/.NET language builder support using componentize-dotnet once the tooling stabilizes.

Current Status

The .NET WASI ecosystem is currently experimental:

• Microsoft removed the wasi-experimental workload from .NET 9 (February 2025)
• .NET 10 does not include native WASI support
• The only option is componentize-dotnet from Bytecode Alliance
• Setup requires experimental NuGet feeds and platform-specific packages
• Path handling bugs exist in the current tooling

Why Deferred

During implementation of #31, we found:

1. Complex setup: Requires experimental NuGet feed (dotnet-experimental)
2. Platform-specific packages: Need different ILCompiler packages per OS
3. Configuration heavy: Many .csproj properties required
4. Tooling bugs: Path handling issues (Windows paths on macOS)
5. Uncertain future: Microsoft appears to have deprioritized WASI

When to Revisit

Monitor these for stability:

• componentize-dotnet releases
• .NET 11+ WASI support announcements
• Microsoft's WASI tracking issues moving back to active milestones

Implementation Notes

When ready, the builder should:

• Check for .NET SDK 9.0+
• Use dotnet build with componentize-dotnet SDK
• Find WASM output in bin/<config>/net<version>/wasi-wasm/
• Provide clear error messages about experimental NuGet feed requirements

Related

• Add Go and C# .NET language support #31 - Go and .NET language support (Go shipped, .NET deferred)
• Auto-install toolchains for language builders #32 - Auto-install toolchains
• Evaluate container-based builds for language compilation #33 - Container-based builds (alternative approach)