:rotating_light: :rotating_light: :rotating_light: Fixing BPE spm converter.
Author: Narsil
Pull request: yes

# What does this PR do?


The spm BPE converter seemed to have been wrong (for quite a while if true).
The merges are recreated from the vocab, but where ordered by their vocab id instead
of the score within spm vocab. It seems to be wrong for Llama.

This PR fixes it.

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Fixes # (issue)


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Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts
- speech models: @sanchit-gandhi
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
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HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
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- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

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Comments:
_The documentation is not available anymore as the PR was closed or merged._

@sgugger 

At least reformer and camembert are concerned (some test failed when writing bogus code here.)

IT's breaking and breaking reformer and xlnet, I removed the breaking part of it for Llama.