Split shade expansion: adjust alpha interpolation to match motion specs

+ Centralizes the interpolation values for easier tweaking in the future
+ Adds more granular control over interpolation of different components:
   - Behind scrim
   - Notification scrim
   - Notifications
   - Notification footer
   - QS

Change-Id: I5e13855e9a5ab5fc0a0c98c3e7293571e515ab8d
Test: Unit tests
Test: Manually on device. See videos
Fixes: 259269166
Fixes: 265643813
Flag: LARGE_SHADE_GRANULAR_ALPHA_INTERPOLATION