Implement launch bounds logic in Android (1/3)

Abstract threading logic that can be shared among persisters into a
common class. Later we'll introduce a new persister that stores mapping
from components to launch params (such as launch bounds and display
unique ID). That persister could reuse this class for threading which
could avoid creating another thread for persistence.

Also added some unit tests for the threading logic.

Bug: 113252871
Test: Manually test that recent tasks can still be restored across
reboots. atest PersisterThreadingTests. TaskPersisterTest is broken in
ToT.

Change-Id: I2b48593f38efcc205c2a213dbd93607c9588b12c