Make it so the artifacts folders register files for cleanup

[baronfel]

Fixes #49582

The SDK knows that it's opting into Artifacts Path, and so the SDK can coordinate correcting the cleanup behavior for ArtifactsPath.

[Copilot]

Pull Request Overview

This PR updates the SDK to properly register files within artifacts folders for cleanup and provides accompanying tests.

• Adds a test in ArtifactsOutputPathTests.cs to verify that published files (e.g., hostfxr.dll) are correctly cleaned up when building in Release configuration.
• Updates the Microsoft.NET.DefaultOutputPaths.targets to include a new target _TrackFileWritesShareableUnderArtifactsPath ensuring file writes under both OutputPath and IntermediateOutputPath are tracked for cleanup.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
test/Microsoft.NET.Build.Tests/ArtifactsOutputPathTests.cs	Adds tests to verify cleanup behavior for artifacts folders
src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.DefaultOutputPaths.targets	Enhances cleanup logic by tracking file writes under artifacts output directories

[dsplaisted]

Instead of duplicating some MSBuild logic, would it make sense to update MSBuild so that (with an opt-in from the SDK) it would also look under the output and intermediate output paths in addition to the project directory?

[baronfel]

That's also very reasonable, and much more clean. I can set that up for sure.

[baronfel]

When dotnet/msbuild#12096 is merged, I'll update this to just set the new property (and keep the existing tests).

[baronfel]

The change has flowed to the VMR this morning, so the next VMR->SDK flow should let us merge this.

[baronfel]

Once #49740 merges this can be rebased and the tests should light up.

[baronfel]

The containers test failures are because Red Hat's registries are undergoing emergency maintenance - nothing actually wrong with the SDK.