Replace _expand_mask with _prepare_4d_attention_mask

[denis-ismailaj]

Fixes #603

[salesforce-cla]

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[denis-ismailaj]

I have signed the CLA

[denis-ismailaj]

This does raise the dependency requirement of LAVIS to be transformers>=4.35 though.
If that is an issue, _expand_mask could be copied instead.

[coffeeexistence]

Updating transformers gives me the following error:

line 24, in __init__
    assert transformers_version < version.parse("4.27"), "BLIP models are not compatible with transformers>=4.27, run pip install transformers==4.25 to downgrade"

[coffeeexistence]

It's worth noting that both modeling_llama.py and modeling_opt.py in this repo have copied _expand_mask from transformers. Perhaps there is an opportunity for consolidation?