join last hidden states of layers for BertForSequenceClassification
Author: dantruonghtno1
Pull request: yes

# What does this PR do?

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Fixes # (issue)


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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_18479). All of your documentation changes will be reflected on that endpoint.

Hey @dantruonghtno1, was this discussed in an issue somewhere? We're very unlikely to merge this as it seems like a niche use-case that adds a number of statements to the code for that specific use-case which could be handled outside of the model.