Refactor bootanimation into a shared lib.

We would like to reuse the animation parts of it in Android things.
This refactors the audio part into the _main and gets callbacks from
the BootAnimation class at interesting times. This will be the same
approach we take to integrate with it.

BUG: 37992717
Test: Built locally and pushed to a bullhead, works with sound.
Change-Id: I5eaca07c25eeb5edeab07d7ae7a29945e0e2cd37