Move unused forked code to external directory (#1192)

* Move unused forked code to external directory

* Fix SLN build errors

* Add back resource provider core since it's referenced by main resource provider project

* Update PackageProjects step of pipeline

external/Microsoft.SqlTools.Hosting.Contracts/Internal/HostingErrorNotification.cs

@@ -0,0 +1,26 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+namespace Microsoft.SqlTools.Hosting.Contracts.Internal
+{
+    /// <summary>
+    /// Parameters to be used for reporting hosting-level errors, such as protocol violations
+    /// </summary>
+    public class HostingErrorParams
+    {
+        /// <summary>
+        /// The message of the error
+        /// </summary>
+        public string Message { get; set; }
+    }
+
+    public class HostingErrorNotification
+    {
+        public static readonly 
+            EventType<HostingErrorParams> Type =
+            EventType<HostingErrorParams>.Create("hosting/error");
+
+    }
+}