DataLoader lifecycle.

- mark disconnected DataLoaders as non-existent (destroyed),
- remove storage destroy on DataLoader destroy,
- more robust destroy on destruct handling,
- less race-conditions.

Bug: b/153874006
Test: atest PackageManagerShellCommandTest PackageManagerShellCommandIncrementalTest IncrementalServiceTest
Change-Id: Ib77302aac546d66ce40c5345417c7b424a1d601b