Job service to expire bitmaps

Bug: 290381858
Test: NotificationTest
Test: NotificationManagerServiceTest
Test: NotificationBitmapJobServiceTest

Test: adb shell device_config put systemui com.android.server.notification.expire_bitmaps true
      send big picture notifications with bitmaps
      wait 24 hours
      => see that bitmaps are removed

Test: do the above with shorter job interval
      => see that removal is silent (no sound, no vibration, no HUN,
         device does not wakeup if dozing)

Change-Id: I06c8a1006fd7030835e41fbf7e06f345e8595150