Move ILVerify tests to run like the ILCompiler.TypeSystem managed tests

[jkoritzinsky]

Fixes #121594

Also remove usage of Newtonsoft.Json and use System.Text.Json instead.

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[Copilot]

Pull request overview

This PR migrates ILVerify tests from the test execution framework to run as managed tests similar to ILCompiler.TypeSystem tests. The main changes include replacing Newtonsoft.Json with System.Text.Json using source generators and restructuring the test project organization.

Key changes:

• Migrated from test framework execution to standard xUnit managed tests
• Replaced Newtonsoft.Json with System.Text.Json and source generation for better performance and AOT compatibility
• Converted IL test projects from legacy format to modern SDK-style projects

Reviewed changes

Copilot reviewed 60 out of 90 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/tests/ilverify/ILVerificationTests.csproj	Removed old test project file (now obsolete)
src/coreclr/tools/ILVerification.Tests/ILVerification.Tests.csproj	New managed test project with proper SDK structure
src/coreclr/tools/ILVerification.Tests/TestDataLoader.cs	Migrated from Newtonsoft.Json to System.Text.Json; changed return types to object[] for xUnit compatibility
src/coreclr/tools/ILVerification.Tests/JsonContext.cs	New source-generated JSON serialization context for AOT compatibility
src/coreclr/tools/ILVerification.Tests/ILMethodTester.cs	New test class for IL method verification tests
src/coreclr/tools/ILVerification.Tests/ILTypeVerificationTester.cs	New test class for type verification tests
src/coreclr/tools/ILVerification.Tests/ILTests/*.ilproj	Converted all IL test projects to modern SDK-style format
src/coreclr/tools/ILVerification.Tests/ILTests/*.il	Added IL test source files in new location
src/coreclr/tools/ILVerification.Tests/ILTests/Directory.Build.props	Build properties for IL test projects
eng/Subsets.props	Added new test project to build system

[jakobbotsch]

Are the instructions in https://github.com/dotnet/runtime/blob/main/src/coreclr/tools/ILVerify/README.md valid after this change?

[jkoritzinsky]

I will update the README.

[jkotas]

Where do these test run after this change in CI? If it is optional leg, should we verify that it is passing?

[jkoritzinsky]

They'll run in the CLR_Tools_Tests job in the runtime pipeline.

Here's where they ran on this PR run: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1220914&view=logs&j=bc555b48-a433-5520-02cb-885a268ad262&t=ac67efe8-e930-5071-5878-22316a6283a4&l=4626

[jkotas]

/ba-g Filled #122228 on the new unrelated failures