bytes_to_unicode was removed from transformers.models.gpt2.tokenization_gpt2
in huggingface/transformers#40936, but it had already been copied into
transformers.convert_slow_tokenizer in huggingface/transformers#30334
(transformers 4.54.1), so import it directly from there.
Applies the same fix to chatglm.py.
* move conversion code to a dedicated conversion directory and split the files akin to the src/models architecture
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Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>