model: EmbeddingGemma Adding Support for SentenceTransformers Dense Modules (#16367)

model: EmbeddingGemma Adding Support for SentenceTransformers Dense Modules (#16367)

* model: EmbeddingGemma sentence-transformers dense linear projections support

* model: add support for EmbeddingGemma SentenceTransformers dense linear projections

Adding support for the Dense modules used in EmbeddingGemma models.
EmbeddingGemma is a SentenceTransformers model with additional modules beyond the base Transformer backbone.

See: https://developers.googleblog.com/en/gemma-explained-embeddinggemma-architecture-and-recipe/

* model: add support for EmbeddingGemma SentenceTransformers dense linear projections

- converting model with dense-layers is optional
- introduced dense config params

* Update convert_hf_to_gguf.py

Co-authored-by: Daniel Bevenius <redacted>
* fixed formatting issues

* Update src/llama-graph.cpp

Co-authored-by: Georgi Gerganov <redacted>
* - removed pooling_type_opt, always allow overriding pooling_type
- asserts checking dense features dims

* fix python lint

* fix ubuntu gcc build warning

* - fixed thread-safety test
- moved asserts to load_hparams

* - tidying up code
- simplifying graph-context expecting both dense weights

* minor : add TODO

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Co-authored-by: Daniel Bevenius <redacted>
Co-authored-by: Georgi Gerganov <redacted>