Use webpack also for small built-in extensions

extensions/gulp/extension.webpack.config.js

@@ -0,0 +1,20 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+//@ts-check
+
+'use strict';
+
+const withDefaults = require('../shared.webpack.config');
+
+module.exports = withDefaults({
+	context: __dirname,
+	entry: {
+		main: './src/main.ts',
+	},
+	resolve: {
+		mainFields: ['module', 'main']
+	}
+});