Only reparent for launch animations.

Returns are currently not affected by the issue, and returning to the
Status Bar creates a flicker when reparenting.

Bug: 202516970
Flag: com.android.systemui.move_transition_animation_layer
Test: atest ActivityTransitionAnimator + manual validation
Change-Id: I011aa9580b528f2e45fd338f0f90a566daa889f6