[`Core tokenization`] `add_dummy_prefix_space` option to help with latest issues (#28010)
* add add_dummy_prefix_space option to slow
* checking kwargs might be better. Should be there for all spm tokenizer IMO
* nits
* fix copies
* more copied
* nits
* add prefix space
* nit
* nits
* Update src/transformers/convert_slow_tokenizer.py
* fix inti
* revert wrong styling
* fix
* nits
* style
* updates
* make sure we use slow tokenizer for conversion instead of looking for the decoder
* support llama ast well
* update llama tokenizer fast
* nits
* nits nits nits
* update the doc
* update
* update to fix tests
* skip unrelated tailing test
* Update src/transformers/convert_slow_tokenizer.py
* add proper testing
* test decode as well
* more testing
* format
* fix llama test
* Apply suggestions from code review