Slice by state in CountMetricProducer

- When a log event is matched to the "what" atom of a metric,
MetricProducer parses the event for state primary key(s) and queries
StateTracker for the correct state values
- CountMetricProducer writes state information to the dump report proto
- Added e2e CountMetric tests that push events to StatsLogProcessor and
check that the resulting dump report is correct

Test: bit statsd_test:*
Bug: 136566566
Bug: 142124705
Change-Id: I9ca5b097151c0c73a617f3b16c8c3584b068cd82