Fix unit tests native dependencies

[ThomasGoulet73]

This is a workaround for dotnet/runtime#111825

Description

Fixes errors in unit tests when trying to load wpfgfx_cor3.dll which depends on D3DCompiler_47_cor3.dll which can't be found at runtime which seems to be caused by a bug in the runtime when using DllImportSearchPath.AssemblyDirectory | DllImportSearchPath.System32 as the search path.

This search path is the default search path used by all projects in this repo and it's configured here:

wpf/eng/WpfArcadeSdk/tools/ExtendedAssemblyInfo.props

Lines 16 to 20 in 81019fc

	<ExtendedAssemblyInfo Include="DefaultDllImportSearchPaths"
	Condition="'$(IncludeDllSafeSearchPathAttribute)'=='true'">
	<Parameter1>DllImportSearchPath.AssemblyDirectory | DllImportSearchPath.System32</Parameter1>
	<IsLiteral1>true</IsLiteral1>
	</ExtendedAssemblyInfo>

We can't just set IncludeDllSafeSearchPathAttribute to false in the test projects since the attribute is used to configure the search path used by default for each assembly. We would need to set it to false for all assemblies trying to load wpfgfx_cor3.dll.

This problem does not occur for apps using WPF, see the issue for more info

Customer Impact

None, test only.

Regression

No.

Testing

Local build + CI + local test.

Risk

None, test only.

Microsoft Reviewers: Open in CodeFlow

[ThomasGoulet73]

@dipeshmsft: This is the workaround I was talking about here: #10304 (comment)

[dipeshmsft]

Thanks @ThomasGoulet73, I took a look at this, and it fixes the issue I was talking about. I am going ahead with the merge. Once again, thanks for investigating this issue.