Fix ALTERNATE_BOUNCER->DREAMING

Alternate bouncer transition was using a different signal, isDreaming,
which would cause confusion and overlap with AOD. Use isAbleToDream
instead.

Also, remove use of sample in favor of StateFlow

Fixes: 443010109
Test: atest FromAlternateBouncerTransitionInteractorTest
Flag: EXEMPT bugfix

Change-Id: Ie605a31ec2349a614aae9a882bacf41acbcecbbd