fix: export serializeLibraryAsJSON from the package (#5017)

src/packages/excalidraw/index.tsx

@@ -183,6 +183,7 @@ export {
   exportToBlob,
   exportToSvg,
   serializeAsJSON,
+  serializeLibraryAsJSON,
   loadLibraryFromBlob,
   loadFromBlob,
   getFreeDrawSvgPath,