feat: add css codesplit inline test

packages/playground/css-codesplit/__tests__/css-codesplit.spec.ts

@@ -3,6 +3,7 @@ import { findAssetFile, getColor, isBuild, readManifest } from '../../testUtils'
 test('should load both stylesheets', async () => {
   expect(await getColor('h1')).toBe('red')
   expect(await getColor('h2')).toBe('blue')
+  expect(await getColor('h3')).toBe('yellow')
 })
 
 if (isBuild) {

packages/playground/css-codesplit/async.css

@@ -0,0 +1,3 @@
+h3 {
+  color: yellow;
+}

packages/playground/css-codesplit/main.js

@@ -1,6 +1,12 @@
 import './style.css'
 import './main.css'
+import('./async.css?inline').then((css) => {
+  const style = document.createElement('style')
+  style.dataset.import = true
+  style.textContent = css.default
+  document.head.appendChild(style)
+})
 
 document.getElementById(
   'app'
-).innerHTML = `<h1>This should be red</h1><h2>This should be blue</h2>`
+).innerHTML = `<h1>This should be red</h1><h2>This should be blue</h2><h3>This should be yellow</h3>`