android : introduce starter project example (#4926)

* Introduce starter project for Android

Based on examples/llama.swiftui.

* Add github workflow

* Set NDK version

* Only build arm64-v8a in CI

* Sync bench code

* Rename CI prop to skip-armeabi-v7a

* Remove unused tests

examples/llama.android/app/src/main/res/values/strings.xml

@@ -0,0 +1,3 @@
+<resources>
+    <string name="app_name">LlamaAndroid</string>
+</resources>