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/IMultiServiceProvider.cs

@@ -0,0 +1,101 @@
+//
+// 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.Collections.Generic;
+using System.Linq;
+using Microsoft.SqlTools.Hosting.Utility;
+
+namespace Microsoft.SqlTools.Hosting.Extensibility
+{
+    public interface IMultiServiceProvider
+    {
+        /// <summary>
+        /// Gets a service of a specific type. It is expected that only 1 instance of this type will be
+        /// available
+        /// </summary>
+        /// <typeparam name="T">Type of service to be found</typeparam>
+        /// <returns>Instance of T or null if not found</returns>
+        /// <exception cref="InvalidOperationException">The input sequence contains more than one element.-or-The input sequence is empty.</exception>
+        T GetService<T>();
+
+        /// <summary>
+        /// Gets a service of a specific type. The first service matching the specified filter will be returned
+        /// available
+        /// </summary>
+        /// <typeparam name="T">Type of service to be found</typeparam>
+        /// <param name="filter">Filter to use in </param>
+        /// <returns>Instance of T or null if not found</returns>
+        /// <exception cref="InvalidOperationException">The input sequence contains more than one element.-or-The input sequence is empty.</exception>
+        T GetService<T>(Predicate<T> filter);
+
+        /// <summary>
+        /// Gets multiple services of a given type
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <returns>An enumerable of matching services</returns>
+        IEnumerable<T> GetServices<T>();
+
+        /// <summary>
+        /// Gets multiple services of a given type, where they match a filter
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="filter"></param>
+        /// <returns></returns>
+        IEnumerable<T> GetServices<T>(Predicate<T> filter);
+    }
+    
+    
+    public abstract class ServiceProviderBase : IMultiServiceProvider
+    {
+
+        public T GetService<T>()
+        {
+            return GetServices<T>().SingleOrDefault();
+        }
+
+        public T GetService<T>(Predicate<T> filter)
+        {
+            Validate.IsNotNull(nameof(filter), filter);
+            return GetServices<T>().SingleOrDefault(t => filter(t));
+        }
+
+        public IEnumerable<T> GetServices<T>(Predicate<T> filter)
+        {
+            Validate.IsNotNull(nameof(filter), filter);
+            return GetServices<T>().Where(t => filter(t));
+        }
+
+        public virtual IEnumerable<T> GetServices<T>()
+        {
+            var services = GetServicesImpl<T>();
+            if (services == null)
+            {
+                return Enumerable.Empty<T>();
+            }
+
+            return services.Select(t =>
+            {
+                InitComposableService(t);
+                return t;
+            });
+        }
+
+        private void InitComposableService<T>(T t)
+        {
+            IComposableService c = t as IComposableService;
+            c?.SetServiceProvider(this);
+        }
+        
+        /// <summary>
+        /// Gets all services using the build in implementation
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <returns></returns>
+        protected abstract IEnumerable<T> GetServicesImpl<T>();
+
+    }
+
+}