Collect background stats: bluetooth, wifi, sensors

Added background times and counts for an app's bluetooth scans, wifi
scans, and sensor usage. Note that the original times for these three
are pooled (i.e. represent the blame apportioned to an app for using
these, rather than the actual time an app used these). Since background
times are not pooled, and are therefore incomparable to the original
times, an extra time, to represent the actual time, had to also be added
in the form of 'total duration' to which background times can be
compared.

Note that this total duration is now a feature of all DurationTimers and
can be used, e.g., to track actual wakelock time (not just
apportioned wakelock times). The total duration is the time used since
reset, and does not give other 'which' times (such as 'since
unplugged').

Bug: 35679958
Bug: 35677312
Bug: 35673525
Test: runtest -x
frameworks/base/core/tests/coretests/src/com/android/internal/os/BatteryStatsTests.java

Change-Id: I4b6943f76517cf5cc9420684857a5592cc7495be