Add animateAddition() to the ViewBoundAnimator API.

The goal is to have a clear API difference between views animating from
not being on screen to being visible and the normal view bound
animations.

Allows the user to specify an origin to the addition animation, and
animates the view starting from that position.

Bug: 224980562
Test: manual and unit tests included
Change-Id: If0e86a3d240582c3e276f76c029cb8d3251e82b0