Convert extension webpack scripts to modules

extensions/git-base/extension-browser.webpack.config.js

@@ -2,15 +2,11 @@
  *  Copyright (c) Microsoft Corporation. All rights reserved.
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
+// @ts-check
+import { browser as withBrowserDefaults } from '../shared.webpack.config.mjs';
 
-//@ts-check
-
-'use strict';
-
-const withBrowserDefaults = require('../shared.webpack.config').browser;
-
-module.exports = withBrowserDefaults({
-	context: __dirname,
+export default withBrowserDefaults({
+	context: import.meta.dirname,
 	entry: {
 		extension: './src/extension.ts'
 	},