Check if the pending cold start is valid periodically.

There are some cases where AMS doesn't notify BroadcastQueue
of process getting killed. Ideally, we should make sure that
BroadcastQueue always get a callback when a process dies but
this should be sufficient to make sure BroadcastQueue doesn't
get stuck.

Bug: 281597599
Test: atest ./services/tests/mockingservicestests/src/com/android/server/am/BroadcastQueueTest.java
Test: atest ./services/tests/mockingservicestests/src/com/android/server/am/BroadcastQueueModernImplTest.java
Change-Id: Ie68388f6122b8ba60a67316a7477686264f7d652