Treat ValueTuple inbox on netstandard2.0 in nupkg

This is necessary to avoid type conflicts.

Author: ericstj

pkg/Microsoft.Private.PackageBaseline/packageIndex.json

@@ -4694,6 +4694,7 @@
       "BaselineVersion": "4.4.0",
       "InboxOn": {
         "netcoreapp2.0": "4.0.2.0",
+        "netstandard2.0": "4.0.2.0",
         "monoandroid10": "Any",
         "monotouch10": "Any",
         "uap10.1": "4.0.2.0",

src/System.ValueTuple/pkg/System.ValueTuple.pkgproj

@@ -6,6 +6,7 @@
       <SupportedFramework>net45;netcore45;netcoreapp1.0;wp8;wpa81;$(AllXamarinFrameworks)</SupportedFramework>
     </ProjectReference>
     <ProjectReference Include="..\src\System.ValueTuple.csproj" />
+    <InboxOnTargetFramework Include="netstandard2.0" />
     <InboxOnTargetFramework Include="netcoreapp2.0" />
     <InboxOnTargetFramework Include="uap10.1" />
     <InboxOnTargetFramework Include="$(AllXamarinFrameworks)" />