Add System.ValueTuple nuget package to fix the issue with build.

Author: oggy22

SampleApps/WebView2WpfBrowser/WebView2WpfBrowser.csproj

@@ -41,5 +41,6 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.Web.WebView2" Version="1.0.1414-prerelease" />
+	<PackageReference Include="System.ValueTuple" Version="4.5.0" />
   </ItemGroup>
 </Project>