Better notebook markup renderer api (#121882)

* Better notebook markup renderer api

For #121256

- Use js modules for notebook output renderers
- Rename apis from `markdown` to `markup`
- Use imports and exports for apis instead of globals for apis
- Use esbuild instead of webpack so we can emit js modules
- Clearly split top level markup renderes from renderers that extend other renderers

* Use constant instead of comment for replacement

extensions/markdown-language-features/webpack.notebook.js

@@ -1,28 +0,0 @@
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-const path = require('path');
-
-module.exports = {
-	mode: 'production',
-	entry: {
-		index: path.join(__dirname, 'notebook', 'index.ts')
-	},
-	module: {
-		rules: [
-			{
-				test: /\.tsx?$/,
-				use: 'ts-loader',
-				exclude: /node_modules/
-			}
-		]
-	},
-	resolve: {
-		extensions: ['.tsx', '.ts', '.js']
-	},
-	output: {
-		filename: '[name].js',
-		path: path.resolve(__dirname, 'notebook-out')
-	}
-};