Post LifetimeExt updates silently

Posts lifetime extension updates silently, by setting
FLAG_ONLY_ALERT_ONCE and setPostSilently.
Note that these updates are sent to System UI whenever a
notification that has been lifetime extended needs to change its
appearance, like transitioning from sending to sent state);
We don't want to alert the user when they just finished sending a direct
reply from the notification, as presumably they'll be looking at the
notification when this happens.

Bug: 329961486
Test: atest NotificationManagerServiceTest.java, build and flash
Flag: ACONFIG android.app.lifetime_extension_refactor STAGING
Change-Id: Iba2c8ac5da826bf970ba6041f1e11b4c50189c4d