Async Initialize CarrierPrivilegesTracker

Create a separate HandlerThread to offload the heavyweight
initialization required for CarrierPrivilegesTracker. Push
all async events to that thread until the init is done, then
process the events in-order and turn down the thread so that
there isn't another unnecessary thread hanging around once
the heavy work is done.

Bug: 357096337
Test: atest CarrierPrivilegesTrackerTest
Flag: async_init_carrier_privileges_tracker
Change-Id: Idba6bc2191183568ad5fb3fd96e4219ea5ddfd99