BroadcastQueue: make "oneway" calls non-blocking.

When an IApplicationThread instance is hosted by the system_server
process, our various schedule-broadcast calls are dispatched as
blocking methods (with the AMS lock held!!), instead of matching the
expected "oneway" contract.

This change offers ProcessRecord.getOnewayThread() which dispatches
calls through FgThread using SameProcessApplicationThread, which
starts with initial support for broadcast-related methods, but could
be expanded in the future where needed.

Bug: 255532202
Test: atest FrameworksMockingServicesTests:BroadcastRecordTest
Test: atest FrameworksMockingServicesTests:BroadcastQueueTest
Test: atest FrameworksMockingServicesTests:BroadcastQueueModernImplTest
Change-Id: I7fb2a7353c44c29cda94e00fc87b8cff6ffc0008