Fix ValueMetric should only pull on real state changes

In ValueMetricProducer, we now map the new and old state values from
onStateChanged to their correct group ids (no mapping happens if the
metric has no state map). We then check if the group ids are the same
and return if they are. Having the same group id means that the state
values are in the same group and no pull is needed.

onStateChanged was updated to take state values stored in FieldValue
objects instead of as ints. This makes it easier to utilize the
mapStateValue function in MetricProducer.

Bug: b/156428844
Test: m statsd_test && adb sync data && adb shell
data/nativetest/statsd_test/statsd_test

Change-Id: Id8f110db593470b8923e7c4259d70cc5f5bc9147