[Whisper] Refactor forced_decoder_ids & prompt ids (#28687)

* up

* Fix more

* Correct more

* Fix more tests

* fix fast tests

* Fix more

* fix more

* push all files

* finish all

* make style

* Fix timestamp wrap

* make style

* make style

* up

* up

* up

* Fix lang detection behavior

* Fix lang detection behavior

* Add lang detection test

* Fix lang detection behavior

* make style

* Update src/transformers/models/whisper/generation_whisper.py

Co-authored-by: Sanchit Gandhi <[email protected]>

* better error message

* make style tests

* add warning

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Co-authored-by: Sanchit Gandhi <[email protected]>