Clean up JS code.

Make some job capabilities (running in Doze, battery saver, and ignoring
network blocking) clearer.
Improve documentation.

Bug: 141645789
Bug: 171305774
Test: atest --rerun-until-failure 5 com.android.server.job.controllers.QuotaControllerTest
Test: atest CtsJobSchedulerTestCases
Change-Id: If276f034ec2284c6b2bb83c6e132f9373827dd49