Migrate dotnet-aot.Tests to MSTest.Sdk on MTP

[Evangelink]

Part of the ongoing xUnit -> MSTest.Sdk (MTP) test migration of the .NET SDK test suite. Migrates the last remaining xUnit test project, dotnet-aot.Tests, to MSTest.Sdk on Microsoft.Testing.Platform.

This project has a NativeAOT publish mode (dotnet publish -p:PublishAotTests=true) that previously relied on the xUnit v3 AOT packages (xunit.v3.core.aot.mtp-v2) and the eng/XUnitV3/XUnitV3.targets machinery. That is replaced by MSTest.Sdk on MTP, whose source generator performs reflection-free test discovery and is NativeAOT-compatible, so the UseXUnitAotPackages property, the UseMicrosoftTestingPlatformRunner override, and the transitive xUnit AOT package exclusions are all removed.

Standard transformations: Microsoft.NET.Sdk -> MSTest.Sdk, the TestFramework project reference -> Microsoft.NET.TestFramework.MSTest, [Fact] -> [TestMethod], xUnit asserts -> MSTest (Empty -> IsEmpty, Equal -> AreEqual, Contains -> FluentAssertions Should().Contain, Skip -> Inconclusive, IsNotType -> an is-type check, Record.Exception -> a local try/catch helper), the AOT [Trait] category -> [TestCategory], CollectionBehavior(DisableTestParallelization = true) -> [assembly: DoNotParallelize] plus an empty MSTestParallelizeScope, and ITestOutputHelper constructor injection replaced with a TestContext-backed output helper.

Verified: the regular build is clean, and dotnet publish -r win-x64 -p:PublishAotTests=true produces a native dotnet-aot.Tests.exe that discovers and lists all tests (the MSTest source generator works under NativeAOT).

[Copilot]

Pull request overview

This PR migrates test/dotnet-aot.Tests from xUnit to MSTest.Sdk running on Microsoft.Testing.Platform (MTP), including support for publishing and executing the test assembly as a NativeAOT binary.

Changes:

• Switch dotnet-aot.Tests to MSTest.Sdk and update project references from Microsoft.NET.TestFramework to Microsoft.NET.TestFramework.MSTest.
• Convert test attributes/assertions from xUnit to MSTest equivalents, including DataRow-based parameterized tests and TestContext-based logging.
• Add assembly-level non-parallelization and override default MSTest method-level parallel settings for this project.

Show a summary per file

File	Description
test/dotnet-aot.Tests/dotnet-aot.Tests.csproj	Switches project to MSTest.Sdk, updates test framework reference, and disables MSTest method-level parallelization for this assembly.
test/dotnet-aot.Tests/AssemblyInfo.cs	Replaces xUnit collection-parallelization config with MSTest [assembly: DoNotParallelize].
test/dotnet-aot.Tests/NativeEntryPointTests.cs	Converts unit tests for NativeEntryPoint.ExecuteCore to MSTest attributes/assertions.
test/dotnet-aot.Tests/DotnetRootResolverTests.cs	Converts resolver tests to MSTest attributes/assertions.
test/dotnet-aot.Tests/AotParserTests.cs	Converts parser tests to MSTest, including local replacement for Record.Exception.
test/dotnet-aot.Tests/AotIntegrationTests.cs	Converts end-to-end “dn” integration tests to MSTest, adds TestContext output helper and cancellation token usage.

Copilot's findings

Comments suppressed due to low confidence (1)

test/dotnet-aot.Tests/AotIntegrationTests.cs:90

• On timeout this returns while stdout/stderr read tasks are still running, and the using var process will dispose the underlying streams. That can lead to background read tasks faulting/unobserved and can also leave child processes running. Consider killing the entire process tree, waiting for exit, and ensuring the read tasks complete before returning.

        if (!process.WaitForExit(timeoutMs))
        {
            process.Kill();
            return (-1, "", "[TIMEOUT]");
        }

• Files reviewed: 6/6 changed files
• Comments generated: 2

[Evangelink]

/ba-g #51530