Android add a new MODEL_TYPE_MULTIMODAL const (#15235)

### Summary
Match const variable name in jni_layer_llama.cpp
`MODEL_TYPE_CATEGORY_MULTIMODAL`

### Test plan
CI

cc @cbilgin

Co-authored-by: Hansong Zhang <[email protected]>

Author: pytorchbot

extension/android/executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmModule.java

@@ -25,6 +25,7 @@ public class LlmModule {
 
   public static final int MODEL_TYPE_TEXT = 1;
   public static final int MODEL_TYPE_TEXT_VISION = 2;
+  public static final int MODEL_TYPE_MULTIMODAL = 2;
 
   private final HybridData mHybridData;
   private static final int DEFAULT_SEQ_LEN = 128;

extension/android/executorch_android/src/main/java/org/pytorch/executorch/extension/llm/LlmModuleConfig.java

@@ -34,6 +34,9 @@ private LlmModuleConfig(Builder builder) {
   /** Model type constant for text-and-vision multimodal models. */
   public static final int MODEL_TYPE_TEXT_VISION = 2;
 
+  /** Model type constant for generic multimodal models. */
+  public static final int MODEL_TYPE_MULTIMODAL = 2;
+
   /**
    * Creates a new Builder instance for constructing LlmModuleConfig objects.
    *
@@ -141,7 +144,7 @@ public Builder dataPath(String dataPath) {
     /**
      * Sets the model type (text-only or multimodal).
      *
-     * @param modelType One of MODEL_TYPE_TEXT or MODEL_TYPE_TEXT_VISION
+     * @param modelType One of MODEL_TYPE_TEXT, MODEL_TYPE_TEXT_VISION, MODEL_TYPE_MULTIMODAL
      * @return This builder instance for method chaining
      */
     public Builder modelType(int modelType) {