Ensure all test projects disable AppHost on macOS

[Copilot]

Dump-related issues on macOS require UseAppHost=false for test projects. This was already applied to the two acceptance integration test projects but missing from the remaining ~45 test projects.

Changes

• Added <UseAppHost Condition="$([MSBuild]::IsOSPlatform('OSX'))">false</UseAppHost> to test/Directory.Build.props
• Removed the now-redundant UseAppHost lines from MSTest.Acceptance.IntegrationTests.csproj and Microsoft.Testing.Platform.Acceptance.IntegrationTests.csproj

This single change in test/Directory.Build.props propagates the setting to all test projects via MSBuild inheritance, replacing the need for per-project declarations.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Ensure all test projects don't use apphost for macOS</issue_title>
<issue_description>To workaround dump-related issues on macOS, we should ensure we have the following in all test projects.

Today we have that already in acceptance test projects.

<UseAppHost Condition="$([MSBuild]::IsOSPlatform('OSX'))">false</UseAppHost>
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Ensure all test projects don't use apphost for macOS #7581

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[Copilot]

Pull request overview

Propagates a macOS-specific MSBuild workaround across the entire test tree by disabling AppHost for all test projects on macOS, removing the need for per-project settings.

Changes:

• Added UseAppHost=false (conditioned on IsOSPlatform('OSX')) to test/Directory.Build.props so it applies to all test projects via inheritance.
• Removed redundant UseAppHost entries from the two acceptance integration test projects.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/Directory.Build.props	Centralizes the macOS AppHost disablement for all test projects.
test/IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests/Microsoft.Testing.Platform.Acceptance.IntegrationTests.csproj	Removes now-redundant per-project UseAppHost setting.
test/IntegrationTests/MSTest.Acceptance.IntegrationTests/MSTest.Acceptance.IntegrationTests.csproj	Removes now-redundant per-project UseAppHost setting.

[Youssef1313]

@Evangelink Now hangdump works correctly :

  Hang dump timeout of '00:15:00' expired
  Dumping process 17542 - dotnet
  The following tests were still running when dump was taken (format: [<time-elapsed-since-start>] <name>):
  [00:16:21] AnsiTerminal_OutputProgressFrameIsCorrect
  Creating dump file '/Users/runner/work/1/s/artifacts/TestResults/Debug/dotnet_17542_hang.dmp'