Include WIFI scan's in Battery Stats.

Call noteWifiScanStartedFromSource() when a scan is started.
Call noteWifiScanStoppedFromSource() when a scan is finished.

The current implementation tracks to UID that requested the scan, and
correctly tracks the duration of the scan. It ignores scan requests
that occur when a scan is already in progress. It does not distinguish
between active and passive scans.

Repurpose all the noteScanWifiLockAcquired/Released() plumbing
for WIFI scan tracking. The WIFI scan locks were never reported
to the user. Use noteFullWifiLock() when WIFI scan locks are used -
this makes sense because the power draw for a WIFI scan lock
should be about the same as for a full WIFI lock.

Bug: 6642581
Change-Id: Ida6e87992853698545b89f875c973a239218317d