Fix Llava conversion for models that use safetensors to store weights
Author: Isotr0py
Pull request: yes

# What does this PR do?

- Some llava variants like [microsoft/llava-med-v1.5-mistral-7b](https://huggingface.co/microsoft/llava-med-v1.5-mistral-7b) use safetensors to store state_dict, even though they are using mistral backbone.
- This PR make the conversion script to be compatible with these models.


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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- [ ] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

@amyeroberts @zucchini-nlp

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- generate: @zucchini-nlp (visual-language models) or @gante (all others)
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- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_35406). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

Awesome, thanks! Let's just wait for a quick re-read from Raushan and I'll let her merge