Fix issue for alignment of pre-tokenized input with BPE, see #150 #154
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Fix an issue with added extra tokens for ensuring the alignment of pre-tokenized input with BPE, see #150
We cover here added tokens introduced by the BPE fallback mechanism for out of vocabulary input character, e.g. "É" resulting in 'Ã', 'ī', which have then confusing offsets when the input is pre-tokenized.
We distinguish transformer tokenizers using BPE/sentencepiece from the other, which is done based on the tokenizer class name. When BPE is used, we examine offsets and tokens in order to filter out added tokens due to the BPE OOV fallback mechanism.
Tested with BERT based models and Roberta based models, more test to come...