Apply dotnet test zero-tests verdict at the whole-run level

[Evangelink]

A test run should not fail just because one module matched no tests when other modules executed successfully. The current per-module exit code aggregation also leaves the terminal summary inconsistent: the command exits successfully, but reports the run as failed.

This change:

• normalizes per-module ZeroTests results before aggregate exit-code calculation
• decides the zero-tests verdict once from the whole-run test count
• treats an empty module as successful in terminal summary accounting while retaining its Exit code: 8 diagnostic
• preserves explicit minimum-test policy failures
• adds end-to-end and focused reporter coverage for an empty module alongside a passing module

This implements the SDK side of microsoft/testfx#7457.

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[Copilot]

Pull request overview

This PR adjusts dotnet test (Microsoft.Testing.Platform path) so that a single module reporting ZeroTests (exit code 8) does not fail an otherwise successful multi-module run, and so the “zero tests ran” verdict is decided once at the whole-run level based on the total executed test count.

Changes:

• Normalize per-module ZeroTests results before aggregate exit-code calculation, and decide whole-run ZeroTests only from the overall TotalTests count.
• Update terminal reporting and exit-code behavior for mixed runs (empty module + passing/failing module).
• Add new test assets and tests to cover the mixed “zero tests + passing” scenario.

Show a summary per file

File	Description
src/Cli/dotnet/Commands/Test/MTP/TestApplicationActionQueue.cs	Normalizes per-module ZeroTests before aggregating exit codes.
src/Cli/dotnet/Commands/Test/MTP/MicrosoftTestingPlatformTestCommand.cs	Applies whole-run ZeroTests verdict based on aggregate TotalTests == 0.
src/Cli/dotnet/Commands/Test/MTP/Terminal/TerminalTestReporter.cs	Treats ZeroTests as success for per-assembly success tracking.
test/dotnet.Tests/CommandTests/Test/TerminalTestReporterTests.cs	Adds focused reporter test for “zero tests + passing” summary behavior.
test/dotnet.Tests/CommandTests/Test/GivenDotnetTestBuildsAndRunsTests.cs	Updates/extends end-to-end tests for mixed-module exit code + summary behavior.
test/TestAssets/TestProjects/MultiTestProjectSolutionWithZeroTestsAndPassingTests/MultiTestProjectSolutionWithZeroTestsAndPassingTests.sln	New multi-project solution test asset for “zero tests + passing tests”.
test/TestAssets/TestProjects/MultiTestProjectSolutionWithZeroTestsAndPassingTests/global.json	Configures test asset to use Microsoft.Testing.Platform runner.
test/TestAssets/TestProjects/MultiTestProjectSolutionWithZeroTestsAndPassingTests/TestProject/TestProject.csproj	New empty-module MTP test project (intentionally produces zero tests).
test/TestAssets/TestProjects/MultiTestProjectSolutionWithZeroTestsAndPassingTests/TestProject/Program.cs	Implements an MTP adapter that publishes no tests (zero-tests module).
test/TestAssets/TestProjects/MultiTestProjectSolutionWithZeroTestsAndPassingTests/AnotherTestProject/AnotherTestProject.csproj	New passing-module MTP test project.
test/TestAssets/TestProjects/MultiTestProjectSolutionWithZeroTestsAndPassingTests/AnotherTestProject/Program.cs	Implements an MTP adapter that publishes a passing test node.

Copilot's findings

• Files reviewed: 11/11 changed files
• Comments generated: 2