Power model calculation based on batterystats data.

Similar to the ActivityReport, the PowerReport contains the power
usage for a device.  To do the calculations, each of the
ComponentActivity objects are called, giving them the whole activity
info (in case they need to apportion blame) and the PowerProfile.
From that, they compute the per-component power usage, which is
then summed up into the AppPower and PowerReport objects.

Test: atest frameworks/base/tools/powermodel --host
Change-Id: Ibc9ada6f7f4a667152fc4af388f04766125ca74c