Move TestNotificationListener to utils

Previously this helper class could only be used for
functional/singleuser tests whereas in its new location it can be used
for other types of tests too. My motivation is to use it in a new
multiuser test case.

Bug: 283100177
Test: atest SafetyCenterNotificationTest
Relnote: N/A
Change-Id: Id2cd0deea2e492039291d3675c21245e5d041517
6 files changed