Use built in function to access special tokens and ids

[MarkusSagen]

Current implementation for mapping the tokens to their ids caused some problems when there were new words containing "token" in them. Currently, we map from the vocab file all tokens containing the word token. However, for (at lease non-SentencePiece) tokenizers in Huggignface transformers, there are already two argmuments for this:

• tokenizer.all_special_tokens
• tokenizer.all_special_ids

Let's test and replace our implementation with the officially supported vocab arguments

tftokenizers/tftokenizers/utils.py

Line 8 in 14dc752

def map_special_tokens_to_ids(