Remove .NET Standard 1.x dependencies

Author: ViktorHofer

eng/Versions.props

@@ -6,8 +6,10 @@
     <!-- Opt-in/out repo features -->
     <UsingToolPdbConverter>false</UsingToolPdbConverter>
     <UsingToolNuGetRepack>true</UsingToolNuGetRepack>
+    <FlagNetStandard1XDependencies>true</FlagNetStandard1XDependencies>
     <!-- Pinned -->
-    <SystemCollectionsImmutableVersion>7.0.0</SystemCollectionsImmutableVersion>
     <MicrosoftDiaSymReaderNativeVersion>17.0.0-beta1.21524.1</MicrosoftDiaSymReaderNativeVersion>
+    <NETStandardLibraryVersion>2.0.3</NETStandardLibraryVersion>
+    <SystemCollectionsImmutableVersion>7.0.0</SystemCollectionsImmutableVersion>
   </PropertyGroup>
 </Project>

src/Directory.Build.targets

@@ -1,3 +1,8 @@
 <Project>
   <Import Project="Sdk.targets" Sdk="Microsoft.DotNet.Arcade.Sdk" />
+
+  <ItemGroup Condition="'$(IsTestProject)' == 'true' or '$(MSBuildProjectName)' == 'TestUtilities'">
+    <!-- Upgrade the NETStandard.Library transitive xunit dependency to avoid transitive 1.x NS dependencies. -->
+    <PackageReference Include="NETStandard.Library" Version="$(NETStandardLibraryVersion)" Condition="'$(TargetFrameworkIdentifier)' != '.NETStandard'" />
+  </ItemGroup>
 </Project>