interface PropKey<T, V : AnimationVector>
Property key of T type.
PropKeys are used when defining a TransitionDefinition, as a part of creating a
state-based animation. Each property (to be animated) needs to be associated with a PropKey of
the type of the property. For example, this creates an alpha property:
val alpha = FloatPropKey(). PropKeys for common data types are
provided out of the box: such as androidx.ui.animation.DpPropKey,
androidx.ui.animation.PxPositionPropKey, etc. To create a custom PropKey of type T, a
typeConverter needs to be supplied to define how the animated data type can be converted to
and from an AnimationVector, so that animations can support multi-dimensional data types.