Add new fields to ScheduledJobStateChanged.

Add priority, prefetch, and num failure fields in order to track
the effectiveness of the feature and policy changes.

Bug: 138239687
Bug: 142272435
Bug: 194532703
Test: atest CtsStatsdAtomHostTestCases:JobSchedulerStatsTests
Change-Id: Id76e9eb872b92ee64baab1898d9acdc08e386f74