docs(pagination-nav): add more examples (#1514)

Adds "Reactive example," "Total," "Shown," and "Custom button text."

docs/src/pages/framed/PaginationNav/PaginationNavReactive.svelte

@@ -0,0 +1,16 @@
+<script>
+  import { PaginationNav, Button } from "carbon-components-svelte";
+
+  let page = 2;
+</script>
+
+<PaginationNav bind:page />
+
+<div style="margin: var(--cds-layout-01) 0">
+  <Button on:click="{() => (page = 0)}" disabled="{page === 0}">
+    Set page to 0
+  </Button>
+</div>
+
+<strong>page:</strong>
+{page}