Add qnn deps to LlamaDemo gradle (#13912)

Now for QNN users, they can use the dependency `implementation
"com.qualcomm.qti:qnn-runtime:$qnnVersion"` to add the runtime deps

Define `qnnVersion` in gradle.properties

Author: kirklandsign

examples/demo-apps/android/LlamaDemo/app/build.gradle.kts

@@ -11,6 +11,8 @@ plugins {
   id("org.jetbrains.kotlin.android")
 }
 
+val qnnVersion: String? = project.findProperty("qnnVersion") as? String
+
 android {
   namespace = "com.example.executorchllamademo"
   compileSdk = 34
@@ -61,6 +63,9 @@ dependencies {
   implementation("com.google.android.material:material:1.12.0")
   implementation("androidx.activity:activity:1.9.0")
   implementation("org.json:json:20250107")
+  if (!qnnVersion.isNullOrEmpty()) {
+    implementation("com.qualcomm.qti:qnn-runtime:$qnnVersion")
+  }
   testImplementation("junit:junit:4.13.2")
   androidTestImplementation("androidx.test.ext:junit:1.1.5")
   androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")

examples/demo-apps/android/LlamaDemo/docs/delegates/qualcomm_README.md

@@ -212,6 +212,8 @@ sh examples/demo-apps/android/LlamaDemo/setup-with-qnn.sh
 This is running the shell script which configures the required core ExecuTorch, Llama2/3, and Android libraries, builds them into AAR, and copies it to the app.
 Note: If you are building the Android app mentioned in the next section on a separate machine (i.e. MacOS but building and exporting for QNN backend on Linux), make sure you copy the aar file generated from setup-with-qnn script to "examples/demo-apps/android/LlamaDemo/app/libs" before building the Android app.
 
+6. Set up the correct QNN version in gradle rule
+Currently, the gralde rule searches for the property `qnnVersion`. When this variable is defined, it will add QNN runtime library to the dependency. To use it, append the string `qnnVersion=<version>` (ex. `qnnVersion=2.37.0`) to the end of the `gradle.properties` file.
 
 ## Run the Android Demo App