Precomputing JobStatus isReady flags.

This switches computing the state of certain explicit and implicit
required constraints from when isReady() is called to when the
constraint changes.

Bug: 111423978
Bug: 117846754
Test: atest com.android.server.job.controllers.JobStatusTest
and atest CtsJobSchedulerTestCases
Change-Id: I39c18d620d7084af5f5713b6259b1f4ed6dafc98