Add `SplinterTokenizer` unit test (#32652)
* add unit tests for splinter_tokenizer
* add unit test for splinter tokenizer, pass in the question_token to be saved on save_pretrained called
* remove unused import
* remove vocab_splinter.txt, add Copied from, use fmt:on and fmt:off to prevent autoformatting on long lines
* remove all the spaces
Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>
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Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>
