Hide test infrastructure from the solution explorer (#38000)

eng/targets/CSharp.Common.props

@@ -16,7 +16,7 @@
     <Reference Include="Microsoft.AspNetCore.Testing" />
     <Reference Include="Moq" />
     <Reference Include="NETStandard.Library" />
-    <Compile Include="$(SharedSourceRoot)test\SuccessfulTests.cs" LinkBase="SharedTests" />
+    <Compile Include="$(SharedSourceRoot)test\SuccessfulTests.cs" LinkBase="SharedTests" Visible="false" />
   </ItemGroup>
 
   <Import Project="$(RepoRoot)src\Testing\src\build\Microsoft.AspNetCore.Testing.props" Condition=" '$(IsTestProject)' == 'true' " />

eng/targets/Helix.targets

@@ -63,10 +63,10 @@
 
   <!-- Item group has to be defined here because Helix.props is evaluated before xunit.runner.console.props  -->
   <ItemGroup Condition="$(BuildHelixPayload)">
-    <Content Include="@(HelixContent)" />
-    <Content Include="$(RepoRoot)eng\scripts\Download.ps1" />
-    <Content Include="$(RepoRoot)NuGet.config" />
-    <Content Include="$(RepoRoot)global.json" />
+    <Content Include="@(HelixContent)" Visible="false" />
+    <Content Include="$(RepoRoot)eng\scripts\Download.ps1" Visible="false" />
+    <Content Include="$(RepoRoot)NuGet.config" Visible="false"  />
+    <Content Include="$(RepoRoot)global.json" Visible="false"  />
     <ContentWithTargetPath Include="
         $(RepoRoot)eng\common\pipeline-logging-functions.*;
         $(RepoRoot)eng\common\tools.*">