Notification: expand flags and defaults in logs

When debugging notification issues, it would be awesome if logs and
dumpsys contained the names of the FLAG_ and DEFAULT_ bits that are set
in flags and defaults, instead of the raw hex values.

Make it so.

Bug: 328572356
Flag: NONE improvement to debug logging
Test: manual
Change-Id: Ia501e100488462c2eea8b50bf977530e53277bd1