Fix recursive calls on DC#ensureActivitiesVisible

Previously CL[1] used display#ensureActivitiesVisible instead of
stack#ensureActivitiesVisible, and it caused recursive calls on
ensureActivitiesVisible in a very hidden way. A possible scenario
is when an activity paused and AM tried to resume another activity
which did not support multi-resume.

[1]: Id8253eb97581a9dd52ab748117d9cd4cc63a206d

fixes: 156189923
Test: atest DisplayContentTests#testEnsureActivitiesVisibleNotRecursive
Change-Id: Iba2a052e4a1d91edfc6fa80954a730ad5ca3ff0d