build: migrate demo from webpack to Vite (#832)

demo/main.ts

@@ -0,0 +1,21 @@
+import { inject } from "@vercel/analytics";
+import { createApp } from "vue";
+import { createPinia } from "pinia";
+import Demo from "./Demo.vue";
+
+const SAMPLE_RATE = 0.5;
+
+inject({
+  beforeSend: event => {
+    if (Math.random() > SAMPLE_RATE) {
+      return null;
+    }
+
+    return event;
+  }
+});
+
+const pinia = createPinia();
+const app = createApp(Demo);
+app.use(pinia);
+app.mount("#app");