Add `min_new_tokens` argument in generate() implementation
Author: silverriver
Pull request: yes

# What does this PR do?

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Fixes #20756 #20814 #20614 (cc @gonced8 @kotikkonstantin)

As many said, it is better to add an argument `min_new_tokens` to the `.generate()` method to limit the length of newly generated tokens. The current parameter `min_length` limits the length of `prompt + newly generated tokens`, not the length of `newly generated tokens`.

It seems that all tests are passed

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Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts and @NielsRogge
- speech models: @sanchit-gandhi

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @sgugger

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- deepspeed: @stas00
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- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

(Note: this PR depends on the resolution of https://github.com/huggingface/transformers/issues/20814, so I'm waiting for it before I review this one)

> (Note: this PR depends on the resolution of #20814, so I'm waiting for it before I review this one)

Great, let me know if there are anything I can help.

Sorry that I have accidently rebased my PR to include the change of #20892. It seems that my operation will link this PR to all pervious commits that have been merged to main.

I think it would be more convenient to make a new PR from the main branch. So I am closing this one. @gante 

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_20819). All of your documentation changes will be reflected on that endpoint.

I have made a new PR #21044