Query Execution: Better exception handling on unawaited async tasks (#502)

* WIP

* This code makes it work!

* Adding similar exception hanling behavior to saving result sets

* Adding unit tests for new extension methods
Auto-cleanup of proj file whitespace

* Implementing changes as per code review comments

src/Microsoft.SqlTools.ServiceLayer/Utility/TaskExtensions.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.Text;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.Utility;
+
+namespace Microsoft.SqlTools.ServiceLayer.Utility
+{
+    public static class TaskExtensions
+    {
+        /// <summary>
+        /// Adds handling to check the Exception field of a task and log it if the task faulted
+        /// </summary>
+        /// <remarks>
+        /// This will effectively swallow exceptions in the task chain. 
+        /// </remarks>
+        /// <param name="task">The task to continue</param>
+        /// <param name="continuationAction">
+        /// An optional operation to perform after exception handling has occurred
+        /// </param>
+        /// <returns>Task with exception handling on continuation</returns>
+        public static Task ContinueWithOnFaulted(this Task task, Action<Task> continuationAction)
+        {
+            return task.ContinueWith(t =>
+            {
+                // If the task hasn't faulted or has an exception, skip processing
+                if (!t.IsFaulted || t.Exception == null)
+                {
+                    return;
+                }
+                
+                // Construct an error message for an aggregate exception and log it
+                StringBuilder sb = new StringBuilder("Unhandled exception(s) in async task:");
+                foreach (Exception e in task.Exception.InnerExceptions)
+                {
+                    sb.AppendLine($"{e.GetType().Name}: {e.Message}");
+                    sb.AppendLine(e.StackTrace);
+                }
+                Logger.Write(LogLevel.Error, sb.ToString());
+
+                // Run the continuation task that was provided
+                continuationAction?.Invoke(t);
+            });
+        }
+    }
+}