supporting different position embeddings
Author: michalozeryflato
Pull request: yes

# What does this PR do?

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Fixes # (issue)


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Models:

- text models: @ArthurZucker and @younesbelkada
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- flax: @sanchit-gandhi
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Comments:
@ArthurZucker @zhangjunyi111 I forked transformers for investigating different positional embeddings in a bioinformatics study.  I created the PR to highlight code changes to my colleagues. I did not intend to suggest merging my code changes into transformers.  I changed the PR to a draft mode. Let me know if I need to delete it.

Closing this PR - was created by mistake

No worries thanks for telling me!