Creates a new `GtkATContext` instance for the given accessible role, accessible instance, and display connection.
The `GtkATContext` implementation being instantiated will depend on the platform.
| accessible_role |
the accessible role used by the `GtkATContext` |
| accessible |
the `GtkAccessible` implementation using the `GtkATContext` |
| display |
the `GdkDisplay` used by the `GtkATContext` |
|
the `GtkATContext` |