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/ExpandRequest.cs

@@ -0,0 +1,76 @@
+//
+// 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.Explorer
+{
+    /// <summary>
+    /// Information returned from a <see cref="ExpandRequest"/>.
+    /// </summary>
+    public class ExpandResponse
+    {
+        /// <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 expanded nodes in the tree
+        /// </summary>
+        public NodeInfo[] Nodes { get; set; }
+
+        /// <summary>
+        /// Path identifying the node to expand. See <see cref="NodeInfo.NodePath"/> for details
+        /// </summary>
+        public string NodePath { get; set; }
+
+        /// <summary>
+        /// Error message returned from the engine for a object explorer expand failure reason, if any.
+        /// </summary>
+        public string ErrorMessage { get; set; }
+    }
+
+    /// <summary>
+    /// Parameters to the <see cref="ExpandRequest"/>.
+    /// </summary>
+    public class ExpandParams
+    {
+        /// <summary>
+        /// The Id returned from a <see cref="CreateSessionRequest"/>. This
+        /// is used to disambiguate between different trees. 
+        /// </summary>
+        public string SessionId { get; set; }
+
+        /// <summary>
+        /// Path identifying the node to expand. See <see cref="NodeInfo.NodePath"/> for details
+        /// </summary>
+        public string NodePath { get; set; }
+    }
+
+    /// <summary>
+    /// A request to expand a node in the tree
+    /// </summary>
+    public class ExpandRequest
+    {
+        /// <summary>
+        /// Returns children of a given node as a <see cref="NodeInfo"/> array.
+        /// </summary>
+        public static readonly
+            RequestType<ExpandParams, bool> Type =
+            RequestType<ExpandParams, bool>.Create("explorer/expand");
+    }
+
+    /// <summary>
+    /// Expand notification mapping entry 
+    /// </summary>
+    public class ExpandCompleteNotification
+    {
+        public static readonly
+            EventType<ExpandResponse> Type =
+            EventType<ExpandResponse>.Create("explorer/expandCompleted");
+    }
+}