Generate using exported model and enable gemma2-2b in ExecuTorch (#33707)
* Generate using exported model and enable gemma2-2b in ExecuTorch
* [run_slow] gemma, gemma2
* truncate expected output message
* Bump required torch version to support gemma2 export
* [run_slow] gemma, gemma2
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Co-authored-by: Guang Yang <guangyang@fb.com>