Enable new endpoints from VSCode side

Author: alexgav

src/razor/src/razorLanguageServerClient.ts

@@ -246,6 +246,8 @@ export class RazorLanguageServerClient implements vscode.Disposable {
             args.push('true');
             args.push('--UpdateBuffersForClosedDocuments');
             args.push('true');
+            args.push('--SingleServerCompletionSupport');
+            args.push('true');
 
             if (options.forceRuntimeCodeGeneration) {
                 args.push('--ForceRuntimeCodeGeneration');