Add task to build extension media (#119294)

This lets us avoid checking in the compiled js files that are used inside webviews and notebooks

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

@@ -6,8 +6,8 @@ const path = require('path');
 
 module.exports = {
 	entry: {
-		index: './preview-src/index.ts',
-		pre: './preview-src/pre.ts'
+		index: path.join(__dirname, 'preview-src', 'index.ts'),
+		pre: path.join(__dirname, 'preview-src', 'pre.ts'),
 	},
 	module: {
 		rules: [