Summary:
Each ComponentDescriptor becomes capable of doing its own interpolation over props for animation purposes.
This new custom interpolator is called by default by the ConcreteComponentDescriptor, but `ComponentDescriptor::interpolateProps` is a virtual function and each ComponentDescriptor can provide custom interpolation if necessary.
For now, only View does any actual interpolation, to support LayoutAnimations.
Changelog: [Internal]
Reviewed By: mdvacca
Differential Revision: D20965310
fbshipit-source-id: e1c1588107848e94c155efecb0da1cc1619ae544