[Notif] Show block message for notif with multiple channels

Showing blocking message on notifications with multiple channels. Also,
the blocking helper was never committing the saveImportance logic...
Updated so it does that again.

Moved binder calls over to bg (for committing block/minimize rules).

Change-Id: I5042cf51a4700958c3cedbf5619fd1cbcb944a03
Fixes: 77320402
Test: Visually, atest {ENR|NotifInfo}Test