[Search][Motion] Modify interpolator for AllApps background scrim

Also rename ANIM_WORKSPACE_SCRIM_FADE to ANIM_SCRIM_FADE since
the scrim is shared between states now.

Bug: 183001675
Test: Manual in 3 button and 0 button modes
Change-Id: Ice83b54480bdf74155e8593c421b68d7186cf78a
4 files changed