Add Phi4 mini instruct

[jackzhxng]

🚀 The feature, motivation and pitch

Implement Phi 4 mini instruct by fitting into llama_transformer.py and export_llama. Should be relatively simple like #8471

Alternatives

No response

Additional context

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RFC (Optional)

No response

cc @mergennachin @iseeyuan @lucylq @helunwencser @tarun292 @kimishpatel

[iseeyuan]

TODO: benchmark and json tokenizer