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/ServerCapabilities/SignatureHelpOptions.cs

@@ -0,0 +1,18 @@
+//
+// 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.DataProtocol.Contracts.ServerCapabilities
+{
+    /// <summary>
+    /// Defines options for signature help that the server supports
+    /// </summary>
+    public class SignatureHelpOptions
+    {
+        /// <summary>
+        /// Characters that trigger signature help automatically
+        /// </summary>
+        public string[] TriggerCharacters { get; set; }
+    }
+}