Add Gemma2 GGUF support (#34002)
* initial setup for ggml.py
* initial setup of GGUFGemma2Converter class
* Add gemma2 model to gguf.md doc
* Partial work on GGUF_TENSOR_MAPPING
* initial setup of GGUF_TENSOR_MAPPING for Gemma2
* refactor: rename GemmaConvert class to GemmaConverter for naming consistency
* feat: complete gemma2 tensor mapping implementation
* feat: add initial implementation of GGUFGemmaConverter
* feat: complete GGUFGemmaConverter implementation
* feat: add test code for gemma2
* refactor: minor code cleanup
* refactor: minor code cleanup
* fix: resolve suggestions
* Update tests/quantization/ggml/test_ggml.py
Co-authored-by: Isotr0py <2037008807@qq.com>
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Co-authored-by: Isotr0py <2037008807@qq.com>
