Create MS.SqlTools.Credentials project (#249)

* Initial credential service files

* Clean-up hostloader

* Update build scripts to build credentials archive

* Move hosting files to new assembly

* Add credentials files to MS.SqlTools.Credentials

* Remove duplicate files

* Update namespace in program.cs

* Fix test build breaks

* Update extensions visibility.

* Remove unused resource strings

* Add xproj files to SLN for appveyor builds

* Fix appveyor build break in test project

* Fix extensibility tests

* Fix various typos in latest iteration

* Add settings for Integration build

* Fix codecoverage.bat to use full pdb for new projects

* Fix bug when packing in folder with native images

* Fix typos in xproj

* Reset XLF to fix build.cmd

src/Microsoft.SqlTools.Hosting/Utility/AsyncContext.cs

@@ -0,0 +1,52 @@
+//
+// 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;
+
+namespace Microsoft.SqlTools.ServiceLayer.Utility
+{
+    /// <summary>
+    /// Simplifies the setup of a SynchronizationContext for the use
+    /// of async calls in the current thread.
+    /// </summary>
+    public static class AsyncContext
+    {
+        /// <summary>
+        /// Starts a new ThreadSynchronizationContext, attaches it to
+        /// the thread, and then runs the given async main function.
+        /// </summary>
+        /// <param name="asyncMainFunc">
+        /// The Task-returning Func which represents the "main" function
+        /// for the thread.
+        /// </param>
+        public static void Start(Func<Task> asyncMainFunc)
+        {
+            // Is there already a synchronization context?
+            if (SynchronizationContext.Current != null)
+            {
+                throw new InvalidOperationException(
+                    "A SynchronizationContext is already assigned on this thread.");
+            }
+
+            // Create and register a synchronization context for this thread
+            var threadSyncContext = new ThreadSynchronizationContext();
+            SynchronizationContext.SetSynchronizationContext(threadSyncContext);
+
+            // Get the main task and act on its completion
+            Task asyncMainTask = asyncMainFunc();
+            asyncMainTask.ContinueWith(
+                t => threadSyncContext.EndLoop(),
+                TaskScheduler.Default);
+
+            // Start the synchronization context's request loop and
+            // wait for the main task to complete
+            threadSyncContext.RunLoopOnCurrentThread();
+            asyncMainTask.GetAwaiter().GetResult();
+        }
+    }
+}
+