Use esbuild instead of webpack to bundle the css extension

Switches from webpack to esbuild to bundle the css extension. Tested this locally in a browser and creating an official build to test the bundled extension still work correctly

extensions/css-language-features/client/tsconfig.browser.json

@@ -0,0 +1,7 @@
+{
+	"extends": "./tsconfig.json",
+	"exclude": [
+		"./src/node/**",
+		"./src/test/**"
+	]
+}