vscode: Add editorconfig to recommended extensions (#13537)

.vscode/extensions.json

@@ -2,6 +2,7 @@
   // See https://go.microsoft.com/fwlink/?LinkId=827846
   // for the documentation about the extensions.json format
   "recommendations": [
+    "editorconfig.editorconfig",
     "ms-azure-devops.azure-pipelines",
     "ms-vscode.cpptools",
     "ms-dotnettools.csharp",