Add lightweight Native AOT essentials sample

[balajibashyam]

Summary

Adds a minimal .NET 10 companion sample for the .NET 8 Essentials: Core Features & Getting Started tutorial.

What's included

• New sample: dotnet-8-essentials/core-features-get-started/ — 10 files

  • WebApplication.CreateSlimBuilder AOT-friendly hosting
  • AOT-compatible singleton DI service (ITextTransformer / TextTransformer)
  • Minimal API endpoints: fixed sample metadata (/), runtime capability (/runtime), typed echo POST (/echo)
  • Source-generated System.Text.Json metadata via AppJsonSerializerContext (all 5 body types registered)
  • Explicit input validation with typed bad-request responses
  • PublishAot=true in the project file (analysis participates during development)
  • 8 managed tests covering JSON context, transformer behavior, endpoints, validation, and 404
  • Zero direct NuGet packages in the application project

• Root README: New sample row + updated .NET 8 Essentials tree (3 siblings)

• GitHub Actions: New test-native-aot-essentials job — installs clang/zlib1g-dev, publishes linux-x64 Native AOT, fails on AOT/trim warnings, executes the native binary directly (not via dotnet), verifies dynamicCodeSupported=false / dynamicCodeCompiled=false, exact JSON responses, and 400 on invalid input

Deliberately omitted (stays in the full tutorial)

Todo CRUD, controllers/MVC, EF Core/databases, Swagger/OpenAPI, reflection fallbacks, benchmarking, performance claims, Docker, authentication, cloud deployment

Versions

• .NET SDK: 10.0.302
• Microsoft.AspNetCore.Mvc.Testing: 10.0.10
• Microsoft.NET.Test.Sdk: 18.8.1
• xunit.v3: 3.2.2
• xunit.runner.visualstudio: 3.1.5
• Application NuGet dependencies: none (only auto-referenced AOT toolchain packages)

Validation

• dotnet restore — passed
• dotnet build --configuration Release — passed (0 errors, 0 warnings)
• dotnet test --configuration Release — passed (8/8)
• Native AOT publish (linux-x64) — passed, no IL2026/IL3050/other warnings
• Native binary executed directly: root JSON exact match; dynamicCodeSupported=false, dynamicCodeCompiled=false; echo {"message":"HELLO NATIVE AOT","length":16}; invalid input → 400
• Application package count: 0
• Security scan — clean
• YAML validation — passed