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/Explorer/CreateSessionRequest.cs

@@ -0,0 +1,65 @@
+//
+// 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;
+using Microsoft.SqlTools.DataProtocol.Contracts.Connection;
+
+namespace Microsoft.SqlTools.DataProtocol.Contracts.Explorer
+{
+    /// <summary>
+    /// Information returned from a <see cref="CreateSessionRequest"/>.
+    /// Contains success information, a <see cref="SessionId"/> to be used when
+    /// requesting expansion of nodes, and a root node to display for this area.
+    /// </summary>
+    public class CreateSessionResponse
+    {
+        /// <summary>
+        /// Unique ID to use when sending any requests for objects in the
+        /// tree under the node
+        /// </summary>
+        public string SessionId { get; set; }
+
+    }
+
+    /// <summary>
+    /// Information returned from a <see cref="CreateSessionRequest"/>.
+    /// Contains success information, a <see cref="SessionId"/> to be used when
+    /// requesting expansion of nodes, and a root node to display for this area.
+    /// </summary>
+    public class SessionCreatedParameters
+    {
+        /// <summary>
+        /// Boolean indicating if the connection was successful
+        /// </summary>
+        public bool Success { get; set; }
+
+        /// <summary>
+        /// Unique ID to use when sending any requests for objects in the
+        /// tree under the node
+        /// </summary>
+        public string SessionId { get; set; }
+
+        /// <summary>
+        /// Information describing the base node in the tree
+        /// </summary>
+        public NodeInfo RootNode { get; set; }
+
+
+        /// <summary>
+        /// Error message returned from the engine for a object explorer session failure reason, if any.
+        /// </summary>
+        public string ErrorMessage { get; set; }
+    }
+    
+    /// <summary>
+    /// Session notification mapping entry 
+    /// </summary>
+    public class CreateSessionCompleteNotification
+    {
+        public static readonly
+            EventType<SessionCreatedParameters> Type =
+            EventType<SessionCreatedParameters>.Create("explorer/sessioncreated");
+    }
+}