[Whisper] Move decoder id method to tokenizer

[sanchit-gandhi]

What does this PR do?

Moves the method get_decoder_prompt_ids from the processor to the tokenizer. The primary reason for this change is that the ASR pipeline class does not load the processor object, but rather the feature extractor and tokenizer separately (see docs). Therefore, as things currently stand, pipeline does not have access to the processor method get_decoder_prompt_ids. By moving it to the tokenizer, it will be able to call this method with pipeline.

Note that this is not a breaking change: we retain a method get_decoder_prompt_ids in the processor. This method simply calls the get_decoder_prompt_ids from the tokenizer:

transformers/src/transformers/models/whisper/processing_whisper.py

Lines 44 to 45 in ca8b332

	def get_decoder_prompt_ids(self, task=None, language=None, no_timestamps=True):
	return self.tokenizer.get_decoder_prompt_ids(task=task, language=language, no_timestamps=no_timestamps)

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[sanchit-gandhi]

Processor's get_decodoer_prompt_ids expected a language code id (e.g. "es"). Tokenizer's set_prefix_tokens expected a language (e.g. "Spanish"). This PR amends the tokenizer method to handle either.

[ArthurZucker]

Very nice thanks a lot! I remember it was temporary so that's a nice follow up!

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Nice fix and thanks for making it fully backward compatible!