Fix broadcast deferral completion refcounting

Also noticed that we haven't properly tracked time spent in some
registered receivers, and that we've been overly aggressive in applying
deferral policy (deferring per individual receiver slot rather than per
broadcast).  Finally, augmented the debug logging in useful ways.

Bug: 125421639
Bug: 123904494
Test: atest MixedManagedProfileOwnerTest#testSupportMessage
Test: tests/ActivityTests
Test: manual (observe trace logging w/ debug on)
Change-Id: I8afdedef6530c296cedc3a4d284853a9dfbb0eb7