Support expired timer information in AnrTimer

When an AnrTimer expires, useful information is saved in an
ExpiredTimer object.  The object is mapped to the timer ID of the
expired timer.  If the timer is discarded, the ExpiredTimer object is
cleaned up along with other associated information.  If the timer is
accepted, the ExpiredTimer object is attached to the TimeoutRecord
(and is then cleaned up).

This CL creates ExpiredTimer as a handle for information.  It does not
add any information.

New unit tests validate that discard/accept behavior.

Flag: EXEMPT refactor
Bug: 407584606
Test: atest
 * FrameworksServicesTests:AnrTimerTest
 * FrameworksServicesTests:com.android.server.am
 * FrameworksMockingServicesTests:com.android.server.am
Change-Id: I74a5f77e89df4e29d4548512c88853e9b87520c7