Add Gemma2 GGUF support
Author: yijun-lee
Pull request: yes

# What does this PR do?

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Add GGUF support for Gemma2
#33260

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Models:

- text models: @ArthurZucker
- vision models: @amyeroberts, @qubvel
- speech models: @ylacombe, @eustlb
- graph models: @clefourrier

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- flax: @sanchit-gandhi
- generate: @zucchini-nlp (visual-language models) or @gante (all others)
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Comments:
@yijun-lee really hoping this gets merged soon 🙏  really need this on our project 

> @yijun-lee really hoping this gets merged soon 🙏 really need this on our project

I’m working on it bit by bit whenever I have time🙂. I’ll make sure to wrap it up soon! Thank you for your interest !

@yijun-lee thank you for your work, this helps a lot of people ! 

Feel free to tag me when this is ready ! 

@SunMarc 
I realize I’ve left this task unattended for quite some time now 😅
But it’s finally complete—I’d greatly appreciate your review!

Thanks for the PR @yijun-lee ! @Isotr0py have a PR that refactor quite a bit the GGUF integration, so that we don't need to specify the tensor mapping. However, we still need the `GGUFGemmaConverter` that you coded. I'll let him review and decide if we merge this before or after his PR gets merged

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