add option to skip special tokens

[ArthurZucker]

Allow skipping special tokens when encoding

fixes #1347, fixes #1391 fixes #1368

[HuggingFaceDocBuilderDev]

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[ArthurZucker]

This works as expected for now:

>>> from transformers import AutoTokenizer
>>> tokenizer = AutoTokenizer.from_pretrained("gp2") 
>>> tokenizer.tokenize("<|endoftext|>")
['<|endoftext|>']

>>> tokenizer._tokenizer.encode_special_tokens = True
>>> tokenizer.tokenize("<|endoftext|>")
['<', '|', 'end', 'of', 'text', '|', '>']

the goal is to support passing this as a kwargs, similarly to the slow!
This way you can both save it and activate it in a __call__.

[ArthurZucker]

TODO :

• Evaluate on a benchmark if this does not slow down too much : good to go
• Add tests
• open a PR in transformers for a followup

[ArthurZucker]

Before merging I just want to add a getter, and make sure we can just set it with tokenizer.encode_special_tokens = True.

[ArthurZucker]

PR is not on the correct branch lol