FXML contains treatAsPrivate stuff that is not prefixed by impl_

In FXML there are methods that are @treatAsPrivate and @Deprecated but are not prefixed by "impl_". This goes against our standards and needs to be fixed. However, some of the methods are used by SceneBuilder (they are marked by the "SB-dependency" comment) so it needs to be discussed with SceneBuilder team.

Moreover, there are treatAsPrivate constructors and even entire classes, we should get rid of them (probably removing constructors in favor of impl_* factory methods and classes in favor of proper internal classes in com.sun package)