Add SDPA and FlashAttention support to T5

[DuyguA]

I made some changes to the T5 modeling file to support new attention interface. I made a bit of rearrangements to employ position_bias correctly into the attention mask.

Fixes #26350

A note though, I made a make fix-copies , however it broke several related models such as longt5 and mt5. Somehow fix script didn't copy over the imports, couldn't grab the attention code correctly hence I skipped that part. If applicable we can merge this PR + I can work on related models in another PR or I'm happy to take some hints to make the script work properly.

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@ArthurZucker @Cyrilvallez @vasqu

[vasqu]

Sorry to be so strict about this but T5 is not a good candidate for flash attention / sdpa. The reason is that the relative attention bias has to be modeled there and as of now, it's not possible with base flash attention (might be possible with sdpa but needs proper mask preparation). tl;dr: It will only support eager attention in the end

We can still refactor this to have the attention interface-like implementation but only for eager in the end (i.e. _supports_sdpa/flash_attn remain False). Wdyt?

[DuyguA]

Sorry to be so strict about this but T5 is not a good candidate for flash attention / sdpa. The reason is that the relative attention bias has to be modeled there and as of now, it's not possible with base flash attention (might be possible with sdpa but needs proper mask preparation). tl;dr: It will only support eager attention in the end

We can still refactor this to have the attention interface-like implementation but only for eager in the end (i.e. _supports_sdpa/flash_attn remain False). Wdyt?

Sounds reasonable to me!

[DuyguA]

Heys again @vasqu , I made the changes for restricting only eager attention. Model tests are passing, only repo consistency checks fail as I mentioned above. PR is ready for merge 😊

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: t5