Use netstandard for coreservices DLL (#676)

* Use netstandard for coreservices DLL
- This is possible thanks to recent updates that target SMO bits using netstandard

* Fix localization failure during dotnet pack
- Namespace changes on SRGen, so updated references to accept the name change

src/Microsoft.SqlTools.Hosting.v2/Utility/ServiceProviderNotSetException.cs

@@ -4,6 +4,7 @@
 //
 
 using System;
+using Microsoft.SqlTools.Hosting.v2;
 
 namespace Microsoft.SqlTools.Hosting.Utility
 {