Statsd broadcast subscriber

Allows a uid that uploads a statsd config to additionally
register a BroadcastSubscriber with statsd. If statsd
detects an anomaly (according to the config's Alert),
statsd can inform a BroadcastSubscriber provided in the config.
The config uses a subscriberId (just an int) to identify the
BroadcastSubscriber. It then uses StatsManager.setBroadcastSubscriber
to associate that subscriberId with a given PendingIntent.
Then, when the anomaly is detected, statsd sends a broadcast
using that PendingIntent, alerting whoever was specified by
the config/setBroadcastSubscriber.

Bug: 70356901
Test: cts-tradefed run cts-dev -m CtsStatsdHostTestCases -t android.cts.statsd.alert.BroadcastSubscriberTests
Change-Id: I4d9ea9a6c8a85e61fadfd99c1513c55abbadd5e9