whisper.objc : enable Core ML in example & fix segmentation fault (#910)

whisper.objc : enable Core ML in example & fix segmentation fault (#910)

* coreml : update endcoder header import path

* coreml : force objc_arc in whisper-encoder.mm

* whisper.objc : create coreml/ group link

* whisper.objc : add coreml model link

* whisper.objc : update readme

* coreml : use -fobjc-arc for coreml/whisper-encoder.mm

* ci: create dummy .mlmodelc for pass ios build

* whisper.objc : update readme

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Co-authored-by: Georgi Gerganov <redacted>