Desktop Mode Taskbar Recreate Animation

This Cl includes
       - addition of entry/exit callback methods in DesktopVisibilityController.
       - taskbar manager now listens to desktop mode changes.
       - TaskbarBackrgroundRedererer can now individually animation backgrounds for transient and persistent taskbars
       - new channel for taskbar icon alpha added to TaskbarViewController
       - new animated float to handle background alpha while we are recreating taskbar with animation.

Solution:

we use the callabck we get from DekstopVisibilty for entry/exit to first change logic of when we are considered inDesktopMode. Upon entry/exit we notify display controller for info change.
we also at notify taskbar manager who is now a listener to the desktop mode change and start the recreate process. TaskbarManager first animates existing taskbar out of user view and then follows the original recreate flow.

Test: Presubmit
Bug: 343882478
Flag: com.android.window.flags.enable_desktop_windowing_mode
Change-Id: Ib827564cacd194f499e7d9b1965e2bb13e3548ab