Build PostSharp with the .NET 11 SDK and Visual Studio 2026

[gfraiteur]

Build and ship PostSharp with the .NET 11 SDK and Visual Studio 2026.

• Support MSBuild 18.9 and 18.10 #91
• Validate the MSBuild integration with the MSBuild server enabled by default #92
• Build PostSharp with the .NET 11 SDK #93
• Raise Roslyn and NetAnalyzers package versions #94
• Verify PostSharp Tools for Visual Studio load in Visual Studio 18.9 and 18.10 #95
• Verify the ahead-of-time compiled dotnet CLI entry point #96

Also worth picking up opportunistically, not tracked separately: the .NET 11 dotnet test options
(--no-dependencies, --timeout, --maximum-failed-tests, --test-modules exclusions, and the
DOTNET_TEST_RUNNER environment variable), and xUnit v3 defaulting to Microsoft.Testing.Platform.
These affect the harness in Tests/, not the product.

Analysis: Documentation/DotNet11-CSharp15-Impact.md in postsharp/PostSharp.

— Claude for Gael