fix: account for libraries v2 when prompting (#4263)

src/components/App.tsx

       if (
         token === this.id ||
         window.confirm(
-          t("alerts.confirmAddLibrary", { numShapes: json.library.length }),
+          t("alerts.confirmAddLibrary", {
+            numShapes: (json.libraryItems || json.library || []).length,
+          }),
         )
       ) {
         await this.library.importLibrary(blob, "published");