Allow Shade to be hidden instantaneously at the end of a launch.

Right now there is a race condition between the time it takes to hide
the Shade and the end of the transition. The delay in the former can
cause flickers.

Bug: 419304171
Flag: com.android.systemui.instant_hide_shade
Test: atest NotificationShadeWindowControllerImplTest ShadeControllerImplTest
Change-Id: I64e985e12d20338a3e5d98c80d324c57e15691bf