Register LLM prefill native method in JNI

We added API in Java. Need to register in JNI as well

Pull Request resolved: #5201

Author: kirklandsign

extension/android/jni/jni_layer_llama.cpp

@@ -285,6 +285,12 @@ class ExecuTorchLlamaJni
         makeNativeMethod("generate", ExecuTorchLlamaJni::generate),
         makeNativeMethod("stop", ExecuTorchLlamaJni::stop),
         makeNativeMethod("load", ExecuTorchLlamaJni::load),
+        makeNativeMethod(
+            "prefillImagesNative", ExecuTorchLlamaJni::prefill_images),
+        makeNativeMethod(
+            "prefillPromptNative", ExecuTorchLlamaJni::prefill_prompt),
+        makeNativeMethod(
+            "generateFromPos", ExecuTorchLlamaJni::generate_from_pos),
     });
   }
 };