llama : add StarCoder2 support (#5795)
* Add support for starcoder2
* handle rope type
* skip rope freq and rotary embeddings from being serialized
* resolve comments
* Update llama.cpp
* remove redundant changes
* handle `rope-theta`
* llama : change starcoder2 rope type
* address comment
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
