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.v2/Extensibility/IStandardMetadata.cs

@@ -0,0 +1,28 @@
+//
+// 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.Extensibility
+{
+    /// <summary>
+    /// Standard Metadata needed for extensions.
+    /// </summary>
+    public interface IStandardMetadata
+    {       
+        /// <summary>
+        /// Extension version. Should be in the format "1.0.0.0" or similar
+        /// </summary>
+        string Version { get; }
+
+        /// <summary>
+        /// Unique Id used to identify the export.
+        /// </summary>
+        string Id { get; }
+
+        /// <summary>
+        /// Optional Display name describing the export type 
+        /// </summary>
+        string DisplayName { get; }
+    }
+}