Fix a small bug around deferring activity visibility

Making the defer specific to the activity instead of "while
transition running". Otherwise, we can break changes in
visibility that don't occur during a transition while a
transition is running (eg. an app becoming visible due to
an on-top app changing translucency).

Bug: 183993924
Test: atest ActivityVisibilityTests#testConvertTranslucentOnNonTopTranslucentActivity
Change-Id: I1589b4d47733ed4182e1e7b5b10fe7957b8dceea