Fix split-shade expansion animation on non-lockscreen.

Before this change, the notifications side was showing much earlier than
the qs side of the shade. The motion spec is for both to show up at the same time.

This is a partial revert of ag/18566290

Test: NotificationPanelViewControllerTest.java
Test: NotificationStackScrollLayoutTest.java
Test: Manually
Bug: 214946307
Change-Id: I013ba4e793c7b5f6c3ec6991b33700e58ee839b5