optimizing for primitive types in animations

The animator classes caused autoboxing by converting primitive types (by far
the most typical types used in animations) to be converted to their
Object equivalents because of various APIs that required Object
(like getValue() to get the animated value). This change creates
factory methods on some classes instead of the former constructors
so that we can create and return private type-specific subclasses
which operate directly on the primitive types instead.

In particular, float and int are natively supported by the animators
now. Support in the APIs for double and long was removed because it
seemed like these less common types did not justify the extra
baggage of the added API and code.

Change-Id: I6008a3883e3d6dd5225005f45f112af148e5a4ea