Accept processor in get_training_chat_template

[qgallouedec]

get_training_chat_template already works on both PreTrainedTokenizer and ProcessorMixin. The type hint, parameter name, and docstring were misleading by saying "tokenizer" only. Call sites (e.g. GRPOTrainer, SFTTrainer) already pass processing_class.

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Note

Low Risk
Low risk API tweak: adds processing_class as the primary parameter with a deprecating alias for tokenizer, so breakage is unlikely but callers passing both args will now error and deprecation warnings may surface.

Overview
get_training_chat_template now takes a processing_class (tokenizer or ProcessorMixin) instead of a tokenizer-only parameter, aligning the type hints and docs with existing processor support.

For backward compatibility it adds a deprecated tokenizer alias that emits a FutureWarning and rejects passing both arguments, and updates internal checks/error messaging to reference the generic processing class/chat template rather than “tokenizer” specifically.

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[albertvillanova]

CI is red:

AttributeError: 'NoneType' object has no attribute 'chat_template'

[albertvillanova]

Thanks.

[albertvillanova]

@qgallouedec, should we consider get_training_chat_template as a public API function?

[qgallouedec]

currently, it is considered public. I don't have strong opinion about it. I was a bit uncertain in the first place, see #5090.