Add fadeIn animation for tiling divider being shown after overview.

A fadeIn animation is only shown when the divider is drawn for the first
time.

This CL changes this behavior and now a fadeIn animation is shown after
entering freeform from Overview.

Flag: com.android.window.flags.enable_tile_resizing

com.android.window.flags.enable_windowing_transition_handlers_observers

com.android.window.flags.enable_windowing_transition_handlers_observers

Test: on device testing, animation now shows after overview

Bug: 402787301
Change-Id: I15927a90ff094d69d3e51acf0b9a5efbdd7c98d8