Improve error message handling (#497)

- Add special handling for token expired errors so they send with a clear flag that'll allow clients to take action on this case
- Send error message instead of callstack for all messages, and ensure all resource manager paths send back inner exceptions so users can understand the true root cause.

src/Microsoft.SqlTools.ResourceProvider.Core/Contracts/FirewallRule.cs

@@ -50,9 +50,11 @@ namespace Microsoft.SqlTools.ResourceProvider.Core.Contracts
   
     }
 
-    public class CreateFirewallRuleResponse
+    public class CreateFirewallRuleResponse : TokenReliantResponse
     {
-        public bool Result { get; set; }
+        /// <summary>
+        /// An error message for why the request failed, if any
+        /// </summary>
         public string ErrorMessage { get; set; }
     }
 
@@ -97,6 +99,4 @@ namespace Microsoft.SqlTools.ResourceProvider.Core.Contracts
         /// </summary>
         public string IpAddress { get; set; }
     }
-
-
 }

src/Microsoft.SqlTools.ResourceProvider.Core/Contracts/TokenReliantResponse.cs

@@ -0,0 +1,28 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Collections.Generic;
+using Microsoft.SqlTools.Hosting.Protocol.Contracts;
+
+namespace Microsoft.SqlTools.ResourceProvider.Core.Contracts
+{
+    /// <summary>
+    /// Any response which relies on a token may indicated that the operation failed due to token being expired.
+    /// All operational response messages should inherit from this class in order to support a standard method for defining
+    /// this failure path
+    /// </summary>
+    public class TokenReliantResponse
+    {
+        /// <summary>
+        /// Did this succeed?
+        /// </summary>
+        public bool Result { get; set; }
+
+        /// <summary>
+        /// If this failed, was it due to a token expiring?
+        /// </summary>
+        public bool IsTokenExpiredFailure { get; set; }
+    }
+}