More RecoverableSecurityException docs.

Mention convenience methods in class docs, and require a valid
NotificationChannel to be provided to match O best-practices.

Also mention that notifyChange() should be triggered when the action
is finished.

Test: builds, boots
Bug: 34676491
Change-Id: I0e6c6d43a93cbce1a5de02621290cc2ff9423274
7 files changed