Collect data from multiple DISPLAY EnergyConsumers

Update MeasuredEnergySnapshot and BatteryExternalStatsWorker to handle
multiple Display EnergyConsumers.

Note: Utilizing the energy consumer data will occur in a follow up CL.

Bug: 194107383
Test: atest FrameworksServicesTests:com.android.server.am.MeasuredEnergySnapshotTest
Test: atest FrameworksServicesTests:BatteryExternalStatsWorkerTes
Change-Id: Ic457b799c0e4ec78e83c1c9559dcfd38027f119a