Pass kwargs to Pipeline's tokenizer call
# What does this PR do?
When calling a Pipeline, the `kwargs` argument is not passed to the tokenizer (it is actually not used at all).
I think the intended behavior is to pass it (as the base tokenizer's `__call__()` method already supports `kwargs`), and that's what this PR does.
[Related to #8180]

The call order is:

```Python3
SpecificPipeline.__call__(..., **kwargs)
# Which calls
Pipeline.__call__(..., **kwargs)
# Which calls
SpecificPipeline._parse_and_tokenize(..., **kwargs)
# Which in turn calls
self.tokenizer(...) # No kwargs in this call
```

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- [x] Did you write any new necessary tests?


## Who can review?
@sgugger @LysandreJik
cc @Narsil who probably knows better.<|||||>Hi @guyrosin , we actually don't want to enable that.
The problem is that kwargs are used both by `_parse_and_tokenize` and by `generate`/`forward`.
See discussion here: https://github.com/huggingface/transformers/pull/9432#discussion_r552550844

I'm guessing you want to override a tokenizer argument at runtime in the pipeline. The best way to do that is to whitelist all arguments of the `tokenizer` (like we did with truncation). and *only* pass `**kwargs` to generate. That's the best way to isolate arguments of both functionalities without creating a mess. **Hopefully** there won't be any arguments with the same name in both function calls..


The `**kwargs` in the function signature, is legacy for now as it simply captures previous arguments that used to be sent, and prevents triggering an error for previously written code.

<|||||>Ohh, got it. Thanks for the explanation @Narsil!