Add What's New section for @xyflow/svelte@1.5.2

Author: github-actions[bot]

sites/svelteflow.dev/src/content/whats-new/2026-03-27.mdx

@@ -0,0 +1,10 @@
+---
+title: "Svelte Flow 1.5.2"
+description: "Changelog for Svelte Flow version 1.5.2"
+authors: [xyflow]
+date: '2026-03-27'
+---
+### Patch Changes
+-   [#5735](https://github.com/xyflow/xyflow/pull/5735) Thanks [@nvie](https://github.com/nvie)! - Allow `type` field to be missing in `BuiltInNode` (no `type` field is the same as `type: "default"`)
+-   [#5723](https://github.com/xyflow/xyflow/pull/5723) Pass options to useReactFlow/useSvelteFlow viewport helper functions correctly
+