Allow apps to bypass Power Save restrictions when launched from a Notification's PendingIntent.

This scenario typically happens when the device is on Doze Mode and a
notification action is triggered from a Wear device.

In a nutshell, the workflow is:

- ProcessRecord has a flag telling whether a process has "whitelist
  management" privileges.
- When NotificationManager binds a new NotificationListenerService, it
  sets the BIND_ALLOW_WHITELIST_MANAGEMENT flag.
- On bind(), ActiveService asserts that only system apps can set that
  flag.
- On computeOomAdjLocked(), ActivityManagerService sets the
  ProcessRecord flag if necessary.
- Upon creating a notification, NotificationManager calls AM to mark its
  PendingIntents as coming from a notification.
- When PendingIntentRecord sends it to the target, it checks if it's
  from a notification and if so calls AM to do the temp whitelist.
- On unbind(), ActiveService removes the ProcessRecord flag if necessary.

Fixes: 28818704

Change-Id: I00d46036a2cbb73f7f733fd35bf0b743a02807a1