Send a Object Explorer session disconnect message on socket exceptions (#739)

* WIP

* WIP 2

* Send disconnect message o binding exception

* Add a try catch around the binding queue error handler

src/Microsoft.SqlTools.ServiceLayer/ObjectExplorer/Contracts/CloseSessionRequest.cs

@@ -39,6 +39,29 @@ namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.Contracts
         public string SessionId { get; set; }
     }
 
+    /// <summary>
+    /// Information returned when a session is disconnected.
+    /// Contains success information and a <see cref="SessionId"/>
+    /// </summary>
+    public class SessionDisconnectedParameters
+    {
+        /// <summary>
+        /// Boolean indicating if the connection was successful
+        /// </summary>
+        public bool Success { get; set; }
+
+        /// <summary>
+        /// Unique ID to use when sending any requests for objects in the
+        /// tree under the node
+        /// </summary>
+        public string SessionId { get; set; }
+
+        /// <summary>
+        /// Error message returned from the engine for a object explorer session failure reason, if any.
+        /// </summary>
+        public string ErrorMessage { get; set; }
+    }
+
     /// <summary>
     /// Establishes an Object Explorer tree session for a specific connection.
     /// This will create a connection to a specific server or database, register
@@ -50,4 +73,14 @@ namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.Contracts
             RequestType<CloseSessionParams, CloseSessionResponse> Type =
             RequestType<CloseSessionParams, CloseSessionResponse>.Create("objectexplorer/closesession");
     }
+    
+    /// <summary>
+    /// Session disconnected notification
+    /// </summary>
+    public class SessionDisconnectedNotification
+    {
+        public static readonly
+            EventType<SessionDisconnectedParameters> Type =
+            EventType<SessionDisconnectedParameters>.Create("objectexplorer/sessiondisconnected");
+    }
 }