Validate `NodeDef`s from `FunctionDefLibrary` of a `GraphDef`.

We already validated `NodeDef`s from a `GraphDef` but missed validating those from the `FunctionDefLibrary`. Thus, some maliciously crafted models could evade detection and cause denial of service due to a `CHECK`-fail.

PiperOrigin-RevId: 332536309
Change-Id: I052efe919ff1fe2f90815e286a1aa4c54c7b94ff