Add WindowsAppSDK reference to sparse sample for MSIX build targets

Author: guimafelipe

Samples/MultiHeadedPackage/cs/cs-wpf-sparse/PrimaryApp/PrimaryApp.csproj

@@ -8,6 +8,11 @@
     <EnableMsixTooling>true</EnableMsixTooling>
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.WindowsAppSDK" />
+    <PackageReference Include="Microsoft.Windows.SDK.BuildTools" />
+  </ItemGroup>
+
   <ItemGroup>
     <AppxManifest Include="Package.appxmanifest">
       <SubType>Designer</SubType>