make battery saver configurable

Add configuration to disable the battery saver.

Bug: 245808850
Fixed: 272527415

Test: atest FrameworksServicesTests:com.android.server.power.PowerManagerServiceTest
atest FrameworksServicesTests:com.android.server.power.NotifierTest

Change-Id: Idb5c42a57e2f77294a7f99cefa86e7c4f9730e41
11 files changed