fix(plugin-nested-docs): prevent phantom breadcrumb row (#13628)

When saving a doc and regenerating the breadcrumbs array, a phantom row
will append itself to the end of the array on save. This is because of
fixes made in #13551 changed the way we merge array and block rows from
the server.

To fix this we need to ensure that row IDs are consistent across form
state invocations, i.e. the hooks that mutate the array rows _cannot_
discard the row IDs.

Before:


https://github.com/user-attachments/assets/db715801-b4fd-4114-b39b-8d9b37fad979

After:


https://github.com/user-attachments/assets/6da63a31-cd5d-43c1-a15e-caddbc540d56

---
- To see the specific tasks where the Asana app for GitHub is being
used, see below:
  - https://app.asana.com/0/0/1211175452200168

next-env.d.ts

@@ -1,5 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
+/// <reference path="./.next/types/routes.d.ts" />
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.