Update battery saver dynamic mode notification

 - Update notification title and summary
 - Present dynamic notification when battery saver triggered by "Based
   on percentage"
 screenshot: https://screenshot.googleplex.com/4AH9ayRB2yDMYFf.png

Bug: 234578979
Test: atest FrameworksMockingServicesTests
Change-Id: I16dbb0a40cc29e2d68e4e0ac2f185661619f3a4d