Use StateListAnimator for AppBarLayout elevation changes

Currently the logic for updating an AppBarLayout's elevation
is baked into the code, and can't be customized. This CL
extracts this into a StateListAnimator which has the added
benefit of now animating the elevation.

BUG: 22008506

Change-Id: I4786a9b56b9f3c18ee0610a16036990939a99101
12 files changed