Use partial evaluation in dotnet test setup

[Evangelink]

Summary

Use MSBuild partial evaluation in two dotnet test setup paths that consume only early evaluation results:

• stop after properties when device handling only needs TargetFramework and TargetFrameworks
• stop after items when the pre-build environment-variable path checks ProjectCapability and IntermediateOutputPath

Core project/module discovery continues to fully evaluate each project and target framework exactly once. MTP applications execute DeployToDevice and ComputeRunArguments, so their ProjectInstance must contain registered targets; partial ProjectInstance evaluation is not resumable and must not be followed by a second full evaluation.

The existing shared EvaluationContext remains scoped across each post-build discovery operation to reuse SDK resolution and filesystem observations between its full project evaluations.

Evaluation lifetime

The pre-build device-selection evaluation and post-build discovery intentionally use different shared evaluation contexts. This prevents filesystem observations cached before the build from hiding imports or generated files created by the build.

The regression test creates a conditional props import during the build and verifies that post-build discovery observes it. It also removes the generated import before each invocation so repeated local runs continue to exercise the cache boundary.

Tests

• ItUsesFreshEvaluationContextAfterBuild
• focused dotnet.Tests coverage for MTP multi-target discovery, traversal/non-test filtering, VSTest non-test handling, and device/environment target execution

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[Copilot]

Pull request overview

This PR updates dotnet test’s Microsoft.Testing.Platform (MTP) project discovery to use MSBuild partial evaluation (stopping after Properties/Items where possible) to reduce discovery-time evaluation work while preserving correctness where full evaluation is required.

Changes:

• Introduces ProjectEvaluationStage-based partial evaluation in MTP discovery, with full evaluation reserved for MTP applications that need target execution.
• Uses partial evaluation when inspecting capabilities/items during build/restore and when selecting a target framework for device scenarios.
• Adds a regression test asset + test to validate post-build discovery observes newly generated imports (fresh evaluation context after build).

Show a summary per file

File	Description
test/TestAssets/TestProjects/DotnetTestDevices/DotnetTestDevices.csproj	Adds a conditional post-build props import and a build-time generator target for the regression scenario.
test/dotnet.Tests/CommandTests/Test/GivenDotnetTestSelectsDevice.cs	Adds a test covering the fresh evaluation context boundary after build.
src/Cli/dotnet/Commands/Test/MTP/SolutionAndProjectUtility.cs	Switches project discovery evaluations to partial stages and re-evaluates to Full when MTP target execution is needed.
src/Cli/dotnet/Commands/Test/MTP/MSBuildUtility.cs	Uses Items-stage evaluation when probing runtime-environment-variable capability during build/restore.
src/Cli/dotnet/Commands/Test/MTP/MicrosoftTestingPlatformTestCommand.cs	Uses Properties-stage evaluation when reading TargetFramework(s) for device-driven framework selection.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 1

[Evangelink]

@ViktorHofer @baronfel I have tried to adopt the partial eval features to dotnet test, please review.