Run PeopleService.onUserUnlocked() on worker thread instead of main thread

This change is targeting on reducing the latency to unlock a user. It
includes these changes:
(1) In DataManager.onUserUnlocked(), execute the listeners registration
code on a worker thread.
(2) Merge the usage stats service query and data persistence to one thread.
(3) Adjust the query events max age from 1 day to 5 mins because we
already persist those events in PeopleService. No need to re-query those
events.

With this change, PeopleService.onUserUnlocked() execution is reduced
from ~200 ms to <1ms. And listeners are set up after conversations being
loaded from the disk. This ensures at the events query time (such as
UsageStatsService query), all the conversations are already available in
People Service to avoid missing some events (events without an
associated conversation are dropped).

Change-Id: I5248afa2771588a2434c335867de4e2d1a2eb6f3
Test: atest com.android.server.people.data.DataManagerTest
Test: atest com.android.server.people.data.ConversationStoreTest
Test: atest com.android.server.people.data.PackageDataTest
Bug: 150733302