Port github extension to use esbuild

Had to make same fixes as with #296355. We can't pull in const enums from a d.ts file like this

extensions/github/extension.webpack.config.js

@@ -1,23 +0,0 @@
-/*---------------------------------------------------------------------------------------------
- *  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 withDefaults from '../shared.webpack.config.mjs';
-
-export default withDefaults({
-	context: import.meta.dirname,
-	entry: {
-		extension: './src/extension.ts'
-	},
-	output: {
-		libraryTarget: 'module',
-		chunkFormat: 'module',
-	},
-	externals: {
-		'vscode': 'module vscode',
-	},
-	experiments: {
-		outputModule: true
-	}
-});