Stop processing jobs whose state hasn't changed.

Only process (check the status) of jobs that the controller says had a
state change. That way, we regularly only process a subset of jobs.

Bug: 138469672
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/job
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/job
Test: atest CtsJobSchedulerTestCases
Change-Id: I866d358797e4745b8ab5b9d855c96ec6006985e0