Convert BatteryUsageStats to and from XML

Bug: 187223764
Test: atest FrameworksCoreTests:BatteryUsageStatsTest#testXml
Change-Id: I6aec09bfb87c1003ede1b24cce8cf474675d2448
Merged-In: I6aec09bfb87c1003ede1b24cce8cf474675d2448
(cherry picked from commit 4b8a26bcaad9049a455b45ca17b51cef555c9cea)
6 files changed