Merge main into live

[dotnet-policy-service]

Please don't squash-merge this PR.

---

Internal previews

📄 File	🔗 Preview link
docs/core/project-sdk/msbuild-props.md	MSBuild reference for .NET SDK projects
docs/core/testing/microsoft-testing-platform-troubleshooting.md	Microsoft.Testing.Platform (MTP) troubleshooting
docs/core/testing/migrating-vstest-microsoft-testing-platform.md	Migrate from VSTest to Microsoft.Testing.Platform (MTP)
docs/core/testing/unit-testing-with-dotnet-test.md	docs/core/testing/unit-testing-with-dotnet-test
docs/core/tools/dotnet-test-mtp.md	dotnet test with Microsoft.Testing.Platform (MTP)
docs/csharp/fundamentals/null-safety/index.md	"Null safety in C#"
docs/csharp/fundamentals/null-safety/null-operators.md	C# null operators
docs/csharp/fundamentals/null-safety/nullable-value-types.md	docs/csharp/fundamentals/null-safety/nullable-value-types
docs/csharp/toc.yml	Taken from https://github.com/dotnet/roslyn/wiki/Samples-and-Walkthroughs

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