Combine state and pendingImmersiveTransitions in

DesktopImmersiveController

Adds all transitions to pendingImmersiveTransitions and uses animation
variable in pendingTransition data class to notify the controller if it
should be animating the transition.

Bug: 380152153
Test: Entering immersive from shell and core
Flag: com.android.window.flags.enable_fully_immersive_in_desktop
Change-Id: Ib8d5c8d486ae8db5831fb3ff22821204a6bdaf27