example vendor app

see comments added in code and Android.bp

We don't have examples of a common Android ecosystem usecase, so
I'm adding one here.

Bug: 227289255
Test: after sepolicy + PRODUCT_PACKAGES:
    11-19 03:14:27.460   488   488 I android.hardware.vibrator-service.example: Vibrator on for timeoutMs: 100
Change-Id: Iee430d85e23c6c8f771dc5aa77bff9be1a91f080