[PIP2] Adds Animation Package and Alpha Animator

As part of pip2, we want to refactor our current animations to
use it's own package. This also adds the alpha enter animator,
with follow up work on the bounds enter / exit animations.

Test: TBD
Flag: enable_pip2_implementation
Bug: 322871963
Change-Id: I56cd46269ccb20caa552a1bd917f9cf706dac191