Allow AnimatedControl to set a value provider

[thephamiliar]

In order to change the colors at runtime for AnimatedControl, we need to expose a method so that the private animatedView can set its value provider.

Main changes are in: d5f1ae0

cc: @thedrick

[thedrick]

This LGTM, thanks for adding this!

@buba447 I wonder if we should keep this approach or just expose the animatedView as a public let?

[thedrick]

Lets merge this through and we can make updates in the future if we feel this isn't sufficient. thanks for adding this @thephamiliar

[DennisWeirauch]

Why is the animationView not exposed from AnimatedControl? I need access to the textProvider from an AnimatedSwitch (with a label indicating the current state "on"/"off").

As there are numerous other cases where properties of the AnimationView need to be accessed from AnimatedControls, the obvious solution would be to directly expose it. Is there a reason not to do so?