[Whisper] Deprecate forced ids for v4.39

[sanchit-gandhi]

What does this PR do?

Supersedes #29433 by deprecating forced decoder ids in preparation for the v4.39 release. The full Whisper CI was run with these changes, where it was confirmed all slow tests passed.

cc @zucchini-nlp @ArthurZucker (and also @gante for generation)

[gante]

LGTM, thank you for the cleanup! 🧼

For a follow-up PR: should we also deprecate ForceTokensLogitsProcessor and its usage? Or is it still used in other places?

[HuggingFaceDocBuilderDev]

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[sanchit-gandhi]

Indeed - Whisper was the only model to use this processor, so we should now deprecate it. Note that since the ForceTokensLogitsProcessor is importable from Transformers as a public class, and given there is currently no deprecation warning, we need to do this in 2-stages again: first with a FutureWarning explaining that this processor will be removed in v4.40, and second with a hard error.

from transformers.generation.logits_process import ForceTokensLogitsProcessor

force_token_map = {1: 2, 3: 2}
logits_processor = ForceTokensLogitsProcessor(force_token_map)

c.f. #29487 for the first stage of deprecation

[zucchini-nlp]

Great, thanks! I did not know that the it will be deprecated this soon 😅