Statsd atom: Power Use

BatteryStats calculates power usage of the device and various components
(such as apps). This information is used, e.g., in the battery panel of
Settings. We now log it to statsd. It can be used for validating how
good the information displayed in Settings is. In the long-term, it is
likely not ideal for off-device calculations, since that can be
hopefully estimated using statsd's raw data.

Three atoms: one for the total power use, one for the power use of each
uid, and one for each non-uid component. Since they will all likely be
pulled together, StatsCompanionService will provide stale data for
BatteryStats pulls called within a second of a previous BatteryStats
pull.

Also in this cl:
Remove StatsLogEventWrapper.writeDouble. Statsd doesn't support actually
writing doubles into its proto reports, so having this function is
misleading (the data will get to statsd and then be completely ignored).
It's less confusing if we don't pretend it does something.

Change-Id: If80bab8ea938afa4632535bb88ff59879fbe8099
Fixes: 119111972
Test: cts-tradefed run cts-dev -m CtsStatsdHostTestCases -t android.cts.statsd.atom.UidAtomTests#testDeviceCalculatedPowerUse
Test: cts-tradefed run cts-dev -m CtsStatsdHostTestCases -t android.cts.statsd.atom.UidAtomTests#testDeviceCalculatedPowerBlameUid
Test: BatteryStatsHelperTest#testDrainTypesSyncedWithProto