Deflake NotificationTemplateViewWrapperTest

Instead of implicitly relying on emptying loopers, we explicitly wait
for condition that the test wants to assert (with proper timeout
handling).

Also TestableLooper thread is used for UiOffloadThread.

Bug: 303799156
Test: 100 iterations passing with Cuttlefish
Change-Id: I1e7be497f36a9ab4699ab7ff6bf7afccbe0df2cb