Support for async components

[dryton]

Vue 3 introduced defineAsyncComponent as a way to create components that load asynchronously:
https://v3.vuejs.org/api/global-api.html#defineasynccomponent

When you pass an async component to the wrapper it will load the component, but it fails to map props from the custom element through to the component.

You can test this out in your demo by updating main.js to:

import { createApp, defineAsyncComponent, h } from "vue";
import wrapper from "vue3-webcomponent-wrapper";
const Counter = defineAsyncComponent(() => import("./components/Counter.vue"));

const webComponent = wrapper(Counter, createApp, h);
window.customElements.define("demo-counter", webComponent);