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/Protocol/IMessageDispatcher.cs

@@ -0,0 +1,72 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.Hosting.Contracts;
+
+namespace Microsoft.SqlTools.Hosting.Protocol
+{
+    /// <summary>
+    /// Interface for objects that can will handle messages. The methods exposed via this interface
+    /// allow users to what to do when a specific message is received.
+    /// </summary>
+    public interface IMessageDispatcher
+    {
+        /// <summary>
+        /// Sets the function to run when a request message of a specific 
+        /// <paramref name="requestType"/> is received
+        /// </summary>
+        /// <param name="requestType">Configuration of the request message <paramref name="requestHandler"/> will handle</param>
+        /// <param name="requestHandler">What to do when a request message of <paramref name="requestType"/> is received</param>
+        /// <param name="overrideExisting">If <c>true</c>, any existing handler will be replaced with this one</param>
+        /// <typeparam name="TParams">Type of the parameters for the request, defined by <paramref name="requestType"/></typeparam>
+        /// <typeparam name="TResult">Type of the response to the request, defined by <paramref name="requestType"/></typeparam>
+        void SetAsyncRequestHandler<TParams, TResult>(
+            RequestType<TParams, TResult> requestType,
+            Func<TParams, RequestContext<TResult>, Task> requestHandler,
+            bool overrideExisting = false);
+        
+        /// <summary>
+        /// Sets the function to run when a request message of a specific 
+        /// <paramref name="requestType"/> is received
+        /// </summary>
+        /// <param name="requestType">Configuration of the request message <paramref name="requestHandler"/> will handle</param>
+        /// <param name="requestHandler">What to do when a request message of <paramref name="requestType"/> is received</param>
+        /// <param name="overrideExisting">If <c>true</c>, any existing handler will be replaced with this one</param>
+        /// <typeparam name="TParams">Type of the parameters for the request, defined by <paramref name="requestType"/></typeparam>
+        /// <typeparam name="TResult">Type of the response to the request, defined by <paramref name="requestType"/></typeparam>
+        void SetRequestHandler<TParams, TResult>(
+            RequestType<TParams, TResult> requestType,
+            Action<TParams, RequestContext<TResult>> requestHandler,
+            bool overrideExisting = false);
+
+        /// <summary>
+        /// Sets the function to run when an event message of a specific configurat
+        /// <paramref name="eventType"/> is received
+        /// </summary>
+        /// <param name="eventType">Configuration of the event message <paramref name="eventHandler"/> will handle</param>
+        /// <param name="eventHandler">What to do when an event message of <paramref name="eventType"/> is received</param>
+        /// <param name="overrideExisting">If <c>true</c>, any existing handler will be replaced with this one</param>
+        /// <typeparam name="TParams">Type of the parameters for the event</typeparam>
+        void SetAsyncEventHandler<TParams>(
+            EventType<TParams> eventType,
+            Func<TParams, EventContext, Task> eventHandler,
+            bool overrideExisting = false);
+
+        /// <summary>
+        /// Sets the function to run when an event message of a specific 
+        /// <paramref name="eventType"/> is received
+        /// </summary>
+        /// <param name="eventType">Configuration of the event message <paramref name="eventHandler"/> will handle</param>
+        /// <param name="eventHandler">What to do when an event message of <paramref name="eventType"/> is received</param>
+        /// <param name="overrideExisting">If <c>true</c>, any existing handler will be replaced with this one</param>
+        /// <typeparam name="TParams">Type of the parameters for the event</typeparam>
+        void SetEventHandler<TParams>(
+            EventType<TParams> eventType,
+            Action<TParams, EventContext> eventHandler,
+            bool overrideExisting = false);
+    }
+}