Add API to whitelist multiple apps at once.

This adds an API to be able to add multiple apps to the power save
whitelist at the same time while only sending out the
POWER_WHITELIST_CHAGNED broadcast once.

Bug: 140141678
Test: atest com.android.server.DeviceIdleControllerTest
Test: atest android.alarmmanager.cts.AppStandbyTests
Change-Id: I66cfd5410b85368647faea704ada1bc1ac563510