docs(toast-notification): add "Autoclose" example

docs/src/pages/framed/ToastNotification/ToastNotificationTimeout.svelte

@@ -0,0 +1,32 @@
+<script>
+  import { Button, ToastNotification } from "carbon-components-svelte";
+  import { fade } from "svelte/transition";
+
+  let timeout = undefined;
+  $: showNotification = timeout !== undefined;
+</script>
+
+<Button
+  disabled="{showNotification}"
+  on:click="{() => {
+    timeout = 3_000; // 3 seconds
+  }}"
+>
+  Show notification
+</Button>
+
+{#if showNotification}
+  <div transition:fade>
+    <ToastNotification
+      timeout="{timeout}"
+      kind="success"
+      title="Success"
+      subtitle="This notification will autoclose in {timeout.toLocaleString()} ms."
+      caption="{new Date().toLocaleString()}"
+      on:close="{(e) => {
+        timeout = undefined;
+        console.log(e.detail.timeout); // true if closed via timeout
+      }}"
+    />
+  </div>
+{/if}