Merge pull request #12248 from glerchundi/fix/csharp-native-libraries-visibility

csharp: hide the native libraries in Visual Studio project explorer

src/csharp/Grpc.Core/Grpc.Core.targets

@@ -4,26 +4,32 @@
     <Content Include="$(MSBuildThisFileDirectory)..\..\runtimes\win\native\grpc_csharp_ext.x86.dll">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       <Link>grpc_csharp_ext.x86.dll</Link>
+      <Visible>false</Visible>
     </Content>
     <Content Include="$(MSBuildThisFileDirectory)..\..\runtimes\win\native\grpc_csharp_ext.x64.dll">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       <Link>grpc_csharp_ext.x64.dll</Link>
+      <Visible>false</Visible>
     </Content>
     <Content Include="$(MSBuildThisFileDirectory)..\..\runtimes\linux\native\libgrpc_csharp_ext.x86.so">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       <Link>libgrpc_csharp_ext.x86.so</Link>
+      <Visible>false</Visible>
     </Content>
     <Content Include="$(MSBuildThisFileDirectory)..\..\runtimes\linux\native\libgrpc_csharp_ext.x64.so">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       <Link>libgrpc_csharp_ext.x64.so</Link>
+      <Visible>false</Visible>
     </Content>
     <Content Include="$(MSBuildThisFileDirectory)..\..\runtimes\osx\native\libgrpc_csharp_ext.x86.dylib">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       <Link>libgrpc_csharp_ext.x86.dylib</Link>
+      <Visible>false</Visible>
     </Content>
     <Content Include="$(MSBuildThisFileDirectory)..\..\runtimes\osx\native\libgrpc_csharp_ext.x64.dylib">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       <Link>libgrpc_csharp_ext.x64.dylib</Link>
+      <Visible>false</Visible>
     </Content>
   </ItemGroup>
 </Project>