add in layer gpt2 tokenizer (#20421)

* add minimal working gpt2 tokenizer

* graph mode and output equivalence tests working

* not today tensorflow. serialization test passing!

* fix style, documentation, docstrings and all that jazz

* passing consistency checks

* move keras nlp to tf dependencies

* fix tf modeling utils and gpt2 attention to enable compiling

* fix (I hope) keras nlp dependencies

* rever changes on generation

* remove debug prints

* remove redundant tf dummy objects

* add from config, get config and max length settings to address review

* let flake ignore the error on distillation you are welcome

* test from config

* add padding test

* address sgugger review

examples/research_projects/seq2seq-distillation/distillation.py

@@ -5,7 +5,7 @@ import gc
 import os
 import sys
 from pathlib import Path
-from typing import List
+from typing import List  # noqa: F401
 
 import pytorch_lightning as pl
 import torch