Do not deliver notifications to frozen processes

If a paused process is sent a notification, the notification is not
delivered but is saved until the process is unpaused.  If there is
already a pending instance of the same notification for the process,
the earlier one is deleted.

If a notfication is sent to a process that is not paused, the
notification is delivered immediately.

Pending notifications are delivered when the proces is unpaused. They
are delivered in the order in which they were posted.

The notifications that are affected by this change are:
 * IApplicationThread.clearDnsCache
 * IApplicationThread.updateTimeZone
 * IApplicationThread.scheduleLowMemory
 * IApplicationThread.updateHttpProxy

Test: atest
 * FrameworksServicesTests:com.android.server.am
 * FrameworksMockingServicesTests:com.android.server.am

Flag: com.android.server.am.defer_binders_when_paused
Bug: 327038797
Change-Id: I17bc1551dfd14684848c2c6573bc736340a858c1