Update the workspace and background scale interpolators.

The spec had a typo (EMPHASIZED_DECELERATE instead of
EMPHASIZED_ACCELERATE). In addition, we're now using LINEAR for the
background since the feel is smoother this way. Cleared with motion
(simonroberts@).

Bug: 232418544
Test: manual
Change-Id: I492dbe8008856d331836793177f1dd58c3265ca2