feat(svelte): add getInternalNode and useInternalNode

packages/svelte/src/lib/hooks/useInternalNode.ts

@@ -0,0 +1,17 @@
+import { derived, type Readable } from 'svelte/store';
+
+import { useStore } from '$lib/store';
+import type { InternalNode } from '$lib/types';
+
+/**
+ * Hook to get an internal node by id.
+ *
+ * @public
+ * @param id - the node id
+ * @returns a readable with an internal node or undefined
+ */
+export function useInternalNode(id: string): Readable<InternalNode | undefined> {
+  const { nodeLookup, nodes } = useStore();
+
+  return derived([nodeLookup, nodes], ([nodeLookup]) => nodeLookup.get(id));
+}