Add target for including NuGet packages in VSIX

Add IncludeNuGetPackageReferences target for including
System.ValueTuple.dll and Newtonsoft.Json.dll in the VSIX.

Author: jcansdale

src/GitHub.VisualStudio/GitHub.VisualStudio.csproj

@@ -180,11 +180,6 @@
       <CustomToolNamespace>GitHub.VisualStudio.Settings</CustomToolNamespace>
       <LastGenOutput>PackageSettingsGen.cs</LastGenOutput>
     </Content>
-    <Content Include="..\..\packages\System.ValueTuple.4.5.0\lib\net461\System.ValueTuple.dll">
-      <Link>System.ValueTuple.dll</Link>
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-      <IncludeInVSIX>true</IncludeInVSIX>
-    </Content>
     <None Include="packages.config">
       <SubType>Designer</SubType>
     </None>
@@ -427,6 +422,13 @@
   <PropertyGroup>
     <UseCodebase>true</UseCodebase>
   </PropertyGroup>
+  <!-- Include required NuGet dependencies-->
+  <Target Name="IncludeNuGetPackageReferences" AfterTargets="GetVsixSourceItems">
+    <ItemGroup>
+      <VSIXSourceItem Include="@(ReferenceCopyLocalPaths)" Condition="'%(ReferenceCopyLocalPaths.NuGetPackageId)' == 'System.ValueTuple'" />
+      <VSIXSourceItem Include="@(ReferenceCopyLocalPaths)" Condition="'%(ReferenceCopyLocalPaths.NuGetPackageId)' == 'Newtonsoft.Json'" />
+    </ItemGroup>
+  </Target>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Import Project="$(VSToolsPath)\VSSDK\Microsoft.VsSDK.targets" Condition="'$(VSToolsPath)' != '' And '$(NCrunch)' != '1'" />
   <Import Project="packaging.targets" />