Move the job scheduler service code to its own jar file.

- Also remove the dependency from SystemServiceRegistry to JobScheduler

See apex/jobscheduler/README_js-mainline.md for the details.

Bug: 137763703
Test: build and boot
Test: atest CtsJobSchedulerTestCases
Change-Id: I2386c78b7a6085d6e543a63f22cb620c4cabd06a