Fix no action menu for split pairs in overview panel

The splitting tasks will be reparented to RecentAnimationSplitTasks
overlay layer in order to animate them together. However, the other
animating apps should also be placed to the same overlay layer so all of
them can be layered properly during the transition.

Fix: 239630217
Test: action menu shows above split pairs in overview panel
Change-Id: Idf4038fe575e37cdf9db16ba672208df45160ec1