BroadcastQueue: more debugging information.

Offer to configure the size of the historical broadcasts retained
for debugging.  Migrate DeviceConfig constants into the "native boot"
namespace so they're available early during system boot when we
allocate structures that can't dynamically change.  Emit all current
constant values during dump.

Misc tests to improve code coverage.

Bug: 250666387
Test: atest FrameworksMockingServicesTests:BroadcastQueueTest
Test: atest FrameworksMockingServicesTests:BroadcastQueueModernImplTest
Change-Id: I01257b4a7e3e21b3c16f34673746df77e9fd9288