Support B&R of notifications in non-system users

- Only backup and restore global state for the system user.
- Ignore user id in data for restore (as user 0 on source device could
be restoring to user 10 on target device for example).
- Don't restore managed services for managed users.

Bug: 123349308
Test: 1) atest $(find \
frameworks/base/services/tests/uiservicestests/src/com/android/server/notification \
-name '*Test.java')
2) Manual: Test backup and restore of DND configurations and app
notifications in system and non-system user.
TODO: More testing
Change-Id: Iea2933f2d8709f830a65815871ce974c00f6ce83