Promote all skin and behavior classes of the default controls to the public API

At the current moment all skins and behaviors for the default controls are residing in the com.sun.javafx.* package. As far as I understand it will not be possible to access that package anymore with version 9, so not possible to access these skins and behaviors.

However, using the existing skin and behavior classes is extremely useful especially when customizing the default controls or extending them to create new ones. Not being able to access the skins and behaviors of the default control would make it close to impossible to extend upon these controls, as it would require to rewrite the complete skin and behavior and then extending that one.

So in the vein of RT-21596 I request that these are promoted to the public API for 9.

Additionally I'd like to note that if they are promoted to the public API, that the skins should receive an additional public constructor the accepts the behavior. See RT-40150 for that one.