BatteryStatsImpl: Support chained attribution for BT events.

These changes are slightly different than the ones for Wifi etc.
We need to keep track of the list of WorkChains attributed to a given
UID in order to log stop events for each of them if the BT process
crashes (or goes away) and we receive a call to noteResetBluetooth..[].

Test: BatteryStatsTests
Bug: 62390666

Change-Id: I4aaa2260cdc509ca08c4fa4838df77cda870ef75