Apply icon alpha animation to expand/collapse private space.

This change is more so to the Alt 3 motion spec:
https://docs.google.com/presentation/d/1zRwJ8cZbwMleXHfC2hX4CJJMGSI954FK0V3ksXl7fyE/edit#slide=id.g2baced0bfd0_1_25

bug: 299294792
bug: 325455879
Test: locally: https://screenshot.googleplex.com/BYCwSH3yRvkkZ3v and https://screenshot.googleplex.com/44byrRx5GUQkncw
manual video:
expand and collapse from header: https://drive.google.com/file/d/1-qRdcbo6lNvUPOx4QWL6wVhTRzl2TVtE/view?usp=sharing
from toast and close container after locking: https://drive.google.com/file/d/1-ix4CcOIzMhsJH3uZdJA1vcV8BvY91T9/view?usp=sharing
Flag: ACONFIG com.android.launcher3.Flags.private_space_animation TRUNKFOOD

Change-Id: I4cde4b8626cf3271880fee697f2fb6bc780eab60