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.UnitTests/UtilityTests/AsyncLockTests.cs

@@ -0,0 +1,50 @@
+//
+// 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;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.Hosting.Utility;
+using NUnit.Framework;
+
+namespace Microsoft.SqlTools.Hosting.UnitTests.UtilityTests
+{
+    [TestFixture]
+    public class AsyncLockTests
+    {
+        [Test]
+        public async Task AsyncLockSynchronizesAccess()
+        {
+            AsyncLock asyncLock = new AsyncLock();
+
+            Task<IDisposable> lockOne = asyncLock.LockAsync();
+            Task<IDisposable> lockTwo = asyncLock.LockAsync();
+
+            Assert.AreEqual(TaskStatus.RanToCompletion, lockOne.Status);
+            Assert.AreEqual(TaskStatus.WaitingForActivation, lockTwo.Status);
+            lockOne.Result.Dispose();
+
+            await lockTwo;
+            Assert.AreEqual(TaskStatus.RanToCompletion, lockTwo.Status);
+        }
+
+        [Test]
+        public void AsyncLockCancelsWhenRequested()
+        {
+            CancellationTokenSource cts = new CancellationTokenSource();
+            AsyncLock asyncLock = new AsyncLock();
+
+            Task<IDisposable> lockOne = asyncLock.LockAsync();
+            Task<IDisposable> lockTwo = asyncLock.LockAsync(cts.Token);
+
+            // Cancel the second lock before the first is released
+            cts.Cancel();
+            lockOne.Result.Dispose();
+
+            Assert.AreEqual(TaskStatus.RanToCompletion, lockOne.Status);
+            Assert.AreEqual(TaskStatus.Canceled, lockTwo.Status);
+        }
+    }
+}