llama : add support for EmbeddingGemma 300m (#15798)

This commit add support for the EmbeddingGemma 300m. This model supports
sliding window attention (SWA) and a new swq_type is introduced to
support symmetric SWA masking.

This commit also extracts the code from the function
llama_is_masked_swa in llama-impl.h, so that the logic can be shared
by both llm_graph_input_attn_no_cache::set_input and
llama_kv_cache::set_input_kq_mask.

With this commit the EmbeddingGemma 300m model can be converted to
to GGUF and used with llama.cpp.

Once the model has been uploaded to HuggingFace it can be used like
this:
```console
./build/bin/llama-cli -hf ggml-org/embeddinggemma-300m-GGUF:Q8_0
```

src/llama-hparams.h

@@ -16,9 +16,10 @@ enum llama_expert_gating_func_type {
 };
 
 enum llama_swa_type {
-    LLAMA_SWA_TYPE_NONE     = 0,
-    LLAMA_SWA_TYPE_STANDARD = 1,
-    LLAMA_SWA_TYPE_CHUNKED  = 2,
+    LLAMA_SWA_TYPE_NONE      = 0,
+    LLAMA_SWA_TYPE_STANDARD  = 1,
+    LLAMA_SWA_TYPE_CHUNKED   = 2,
+    LLAMA_SWA_TYPE_SYMMETRIC = 3,
 };
 
 struct llama_hparams_posnet {
@@ -227,6 +228,8 @@ struct llama_hparams {
 
     // number of layers for which has_kv() returns true
     uint32_t n_layer_kv() const;
+
+    bool is_masked_swa(llama_pos p0, llama_pos p1) const;
 };
 
 static_assert(std::is_trivially_copyable<llama_hparams>::value, "llama_hparams must be trivially copyable");