Use libman feed for VS internal packages

The msft_consupmtion feed does not retail older package versions, so the
build dependencies that were once there are no longer.

nuget.config

@@ -4,7 +4,7 @@
     <clear />
     <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
     <add key="dotnet-myget-legacy" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/myget-legacy/nuget/v3/index.json" />
-    <add key="vs" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/msft_consumption/nuget/v3/index.json" />
+    <add key="libman" value="https://pkgs.dev.azure.com/azure-public/vswebtools/_packaging/libman/nuget/v3/index.json" />
   </packageSources>
 
   <packageSourceMapping>
@@ -14,7 +14,7 @@
     <packageSource key="dotnet-myget-legacy">
       <package pattern="Microsoft.Extensions.CommandLineUtils.Sources" />
     </packageSource>
-    <packageSource key="vs">
+    <packageSource key="libman">
       <package pattern="Microsoft.Test.Apex.VisualStudio" />
       <package pattern="Microsoft.VisualStudio.Internal.MicroBuild" />
       <package pattern="Microsoft.WebTools.Languages.*" />