BLE scan API using PendingIntent

This allows apps to listen for beacons, etc., without having to
run a foreground service and register a callback. They can instead
register a PendingIntent which will be fired when scan results
are available or when an error occurs.

Bug: 37254611
Test: WIP
Change-Id: I1793eee67ff0211370ed6fc38be4d95a4c5853f5