API changes for DownloadManager and JobScheduler.

To support moving DownloadManager, add new JobScheduler network type
constraint that matches "any network except roaming."  Also add an
API to get a specific JobInfo by ID.

Since the default network can be different on a per-app basis, and
individual apps may be blocked due to app standby, evaluate job
connectivity constraints on a per-UID basis.  To implement this
cleanly, add NetworkInfo.isMetered() to match the isRoaming() API.

Add new DownloadManager APIs to support charging and device idle
constraints, which are plumbed through to JobScheduler under the
hood when scheduled.

Add filtering to JobScheduler dumpsys to omit noisy details for
packages the caller isn't interested in.

Bug: 28098882, 26571724, 19821935
Change-Id: I09ca7184ef7ce6adba399f579d415a5fb2ea6110