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.DataProtocol.Contracts/Connection/LanguageFlavorChange.cs

@@ -0,0 +1,42 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Microsoft.SqlTools.Hosting.Contracts;
+
+namespace Microsoft.SqlTools.DataProtocol.Contracts.Connection
+{
+
+    /// <summary>
+    /// Parameters for the Language Flavor Change notification.
+    /// </summary>
+    public class LanguageFlavorChangeParams
+    {
+        /// <summary>
+        /// A URI identifying the affected resource         
+        /// </summary>
+        public string Uri { get; set; }
+
+        /// <summary>
+        /// The primary language
+        /// </summary>
+        public string Language { get; set; }
+
+        /// <summary>
+        /// The specific language flavor that is being set
+        /// </summary>
+        public string Flavor { get; set; }
+    }
+
+    /// <summary>
+    /// Defines an event that is sent from the client to notify that
+    /// the client is exiting and the server should as well.
+    /// </summary>
+    public class LanguageFlavorChangeNotification
+    {
+        public static readonly
+            EventType<LanguageFlavorChangeParams> Type =
+            EventType<LanguageFlavorChangeParams>.Create("connection/languageflavorchanged");
+    }
+}