Send EvaluateRequest after execution completes

This change modifies the way the EvaluateRequest message is handled in the
LanguageServer.  Previously the evaluation response would be sent back
immediately since we aren't giving back an actual result.  This behavior
is now changed to wait until execution completes before sending the
response so that the caller knows when execution has completed.

Author: daviwil

src/PowerShellEditorServices.Protocol/Server/LanguageServer.cs

@@ -737,7 +737,7 @@ private bool IsQueryMatch(string query, string symbolName)
             return symbolName.IndexOf(query, StringComparison.OrdinalIgnoreCase) >= 0;
         }
 
-        protected async Task HandleEvaluateRequest(
+        protected Task HandleEvaluateRequest(
             DebugAdapterMessages.EvaluateRequestArguments evaluateParams,
             RequestContext<DebugAdapterMessages.EvaluateResponseBody> requestContext)
         {
@@ -749,16 +749,25 @@ protected async Task HandleEvaluateRequest(
                 this.editorSession.PowerShellContext.ExecuteScriptString(
                     evaluateParams.Expression,
                     true,
-                    true).ConfigureAwait(false);
+                    true);
 
-            // Return an empty result since the result value is irrelevant
-            // for this request in the LanguageServer
-            await requestContext.SendResult(
-                new DebugAdapterMessages.EvaluateResponseBody
+            // Return the execution result after the task completes so that the
+            // caller knows when command execution completed.
+            executeTask.ContinueWith(
+                (task) =>
                 {
-                    Result = "",
-                    VariablesReference = 0
+                    // Return an empty result since the result value is irrelevant
+                    // for this request in the LanguageServer
+                    return
+                        requestContext.SendResult(
+                            new DebugAdapterMessages.EvaluateResponseBody
+                            {
+                                Result = "",
+                                VariablesReference = 0
+                            });
                 });
+
+            return Task.FromResult(true);
         }
 
         #endregion