Send loading tasks to PersisterQueue

LaunchParamsModifier can then use PersisterQueue to load tasks, instead
of blocking the thread UserController uses to broadcast user state
changes.

Also made a few small optimizations.

Bug: 365983567
Test: Settings launches at the right location after reboot.
Test: atest LaunchParamsPersisterTests
Test: atest PersisterQueueTests
Flag: EXEMPT bug fix
Change-Id: Ia43d0298c912f7f8ab3444a4c4d7a1d38639a23d