add async wrapper to sandbox

Author: Rich-Harris

playgrounds/sandbox/Wrapper.svelte

@@ -0,0 +1,9 @@
+<script>
+	import App from './src/App.svelte';
+</script>
+
+<svelte:boundary>
+	<App />
+
+	{#snippet pending()}{/snippet}
+</svelte:boundary>

playgrounds/sandbox/index.html

@@ -12,7 +12,7 @@
 
 		<script type="module">
 			import { mount, hydrate, unmount } from 'svelte';
-			import App from '/src/App.svelte';
+			import App from '/Wrapper.svelte';
 
 			globalThis.delayed = (v, ms = 1000) => {
 				return new Promise((f) => {