I suggest creating a feature request for defining standard key combinations in the JavaFX issue tracker.
That way, when Behaviors are made public they can make use of the standard key combination API.
JavaFX has a behavior system to model platform specific behaviors such as key events and mouse events. The behavior API is currently private and will (likely) be exposed as a public API in a future JavaFX release (after it has undergone, more development, modification and review). The key bindings in the behaviors are the closest thing to the standard key combinations you refer to. You can see how some key bindings are defined in the ListViewBehavior. Many of the standard bindings defined in QT are to do with text input bindings, so the equivalent of those is the TextInputBinding. Be aware that because classes like TextInputBinding are not supported public API, they will be subject to change without notice in future JavaFX versions.
Some common keys like next track, previous track, volume up, volume down, etc, are defined in the existing KeyCombination class.